LEISURE TRAVEL VANS UNITY – Roof Seal and Skylight Maintenance

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Roof Seal and Skylight Maintenance for LEISURE TRAVEL VANS UNITY

The LTV Unity’s fiberglass roof cap sits atop a Mercedes-Benz Sprinter 3500 chassis and sees more thermal cycling than most owners expect — desert sun to mountain cold in a single trip. The cab-over lounger skylight is the Unity’s single most common leak point: it sits in a recessed well at the front of the roof cap, collects standing water, and its factory sealant cracks within 2–3 seasons. Catching a failure early means a $40 tube of sealant; ignoring it means delaminated cab-over ceiling panels and potential damage to the wiring routed through that area. This guide walks you through a full roof inspection, skylight reseal, and protective coating — doable in a weekend with basic tools.

Required Parts

Step-by-Step Instructions

Step 1: Set Up Safely and Access the Roof

Park the Unity on level ground, set the parking brake, and chock the rear wheels — the Sprinter 3500 dual-rear-wheel stance is stable, but a 13-foot roof fall is fatal. Turn off your Xantrex Freedom XC 2000W inverter at the command center panel and disconnect shore power at the TT-30 inlet (passenger-side exterior, forward of the rear wheel well) before going topside. Any roof work near the solar prep conduit termination points risks damaging wiring if you’re kneeling on it uninformed. Use a stabilized ladder rated for your weight plus tools — position it at the rear corner away from the Fiamma F45s cassette housing above the passenger sliding door, since that upper frame rail area is not a load-bearing step point. Once on the roof, lay down a kneeling pad to distribute your weight across the fiberglass cap rather than point-loading it. Walk only on the reinforced perimeter edges and the center spine between the MaxxFan Deluxe vent and the skylight well — avoid stepping directly on either curb or street-side edges near the solar prep knockout plates, which are thinner unsupported sections.

Step 2: Inspect the Full Roof Cap for Damage and Separation

Start at the front cab-over skylight well and work methodically toward the rear. The Unity’s fiberglass roof cap bonds to the Sprinter body at a seam that runs along both sides just above the Fiamma F45s rail line — press this seam every 12 inches with your thumb; any sponginess or hollow sound indicates water has already infiltrated the bond. At the skylight, look for the telltale ‘alligatoring’ pattern where white Dicor lap sealant has dried, cracked, and pulled away from the curb frame — this is almost always visible within 18–24 months on vans stored outdoors. Probe the sealant bead around the MaxxFan Deluxe curb with your fingernail: healthy sealant is slightly tacky and flexible; failed sealant snaps or crumbles. Check the solar prep conduit fittings (typically two, mounted toward the street side of the roof cap, roughly centered fore-to-aft) for lifted edges or gaps. Inspect all four corners of the fiberglass cap where it meets the Sprinter’s painted steel — this transition is sealed at the factory with a brush-applied compound that becomes brittle. Note every suspect area with painter’s tape flags before you descend; you will lose track of small cracks when re-climbing.

Step 3: Clean the Entire Roof Surface

Proper adhesion of new sealant and coating depends entirely on a clean, oil-free surface — skip this step and your EternaBond tape will peel within one season. Mix the Dicor rubber roof cleaner and degreaser at the dilution marked on the label (typically 1:4 with water) and apply it with a soft-bristle brush in 4-foot sections, scrubbing in a circular motion. Pay extra attention to the skylight well, which traps organic debris and develops a black biofilm that looks like a shadow but is actually mold — it prevents sealant adhesion completely. Rinse with low-pressure water (a garden hose is fine; never use a pressure washer on the fiberglass cap seams). Clean around the MaxxFan Deluxe curb, the solar conduit fittings, and the full perimeter seam with a detail brush to get into the radius where old sealant meets the roof surface. After rinsing, give the roof a full 2-hour dry time in direct sun, or 4 hours in shade — Dicor lap sealant and EternaBond both specify a dry, ambient-temperature surface for proper cure. Wipe any remaining residue near the cab-over skylight with isopropyl alcohol on a clean rag before proceeding.

Step 4: Remove Failed Sealant and Prep the Skylight Curb

The cab-over skylight on the Unity sits in a molded fiberglass well approximately 24 inches wide by 18 inches deep (fore-to-aft). The skylight dome is secured to an ABS plastic curb frame, which is then bedded and lapped onto the fiberglass roof cap — there are two distinct sealant interfaces to address. Using the plastic putty knife (not metal — metal will gouge the fiberglass and create new leak paths), carefully lift and peel the old Dicor lap sealant bead from both the top edge of the curb-to-dome joint and the lower curb-to-roof-cap joint. Work slowly around the full perimeter; you are not trying to remove every trace of old sealant, only the cracked, lifted, and non-adhering sections. If you encounter a section where old sealant is still firmly bonded, leave it — cutting into good adhesion weakens your repair. Once loose material is removed, use the plastic putty knife edge to lightly scuff the remaining sealant surface for mechanical adhesion. Wipe the entire skylight curb perimeter with isopropyl alcohol. Check the four mounting screw locations on the curb corners — if any screws are backed out or the curb rocks, retighten with a #2 Phillips before sealing, because no amount of sealant compensates for a loose mechanical connection.

Step 5: Apply EternaBond Tape to the Skylight and Critical Seams

EternaBond RoofSeal tape is your primary waterproofing layer — the Dicor lap sealant you apply afterward is the weather-exposed top coat, not the seal itself. Cut strips from the 4-inch roll to match each side of the skylight curb, adding 2 inches of overlap at each corner. Peel back only the first 3 inches of the release liner, position the tape with the edge centered over the curb-to-roof-cap joint, then slowly peel the liner while pressing the tape flat with your palm in a continuous motion — do not stretch the tape, as it will spring back and create bridging. At corners, make diagonal relief cuts in the tape to allow it to lie flat without wrinkling; overlapping corner patches eliminate gaps. Use the J-roller with firm pressure over every inch of applied tape — two full passes, the second perpendicular to the first. The tape will feel secure immediately but reaches full adhesion in 24 hours. Apply EternaBond strips to the solar prep conduit fittings using the same technique, cutting a cross-slit pattern to wrap the fitting base. Do not apply EternaBond over the MaxxFan Deluxe hinge side — the vent lid needs to open, so tape that perimeter with Dicor only.

Step 6: Apply Dicor Lap Sealant Over All Seams and Penetrations

Load the self-leveling Dicor lap sealant into the drip-free caulking gun — the drip-free mechanism matters here because Dicor is very fluid at temperatures above 70°F and will run out of the tip between cuts. Apply a generous, continuous bead along every EternaBond tape edge, both sides of the MaxxFan Deluxe curb perimeter, the solar conduit fittings, and the full perimeter roof cap seam where fiberglass meets painted Sprinter steel. ‘Self-leveling’ means this product is designed to flow out and self-smooth on horizontal surfaces — do not try to tool it with a putty knife, as you will create voids. On vertical or near-vertical surfaces (the front and rear walls of the cab-over skylight well), hold the tube nozzle at a 45-degree angle and apply a slightly thicker bead, then tool immediately with a moistened finger before the sealant skins over. The goal is a bead that bridges from the tape edge onto the adjacent roof surface by at least three-quarters of an inch on both sides. One 10.3-ounce tube will cover the skylight and MaxxFan perimeters; have a second tube on hand for the conduit fittings and perimeter seam. Allow the Dicor to cure for a full 24 hours before proceeding to coating.

Step 7: Apply EPDM Rubber Roof Coating to the Full Cap

Coat the entire fiberglass roof cap with EPDM rubber coating to unify the repaired areas, reflect UV, and add a final waterproofing layer. First, roll the Liquid Rubber EPDM/TPO primer across the full roof surface using the 3-inch roller in overlapping W-pattern strokes — the primer is critical for adhesion to fiberglass and to the existing factory coating; do not skip it. Allow the primer to tack up per the label (typically 30–60 minutes at 75°F). Apply the EPDM rubber coating in two coats using the clean 3-inch roller: the first coat should be thin and even, worked into any surface texture, allowed to cure 4 hours. The second coat goes on perpendicular to the first for uniform coverage. Apply coating over the Dicor sealant beads — the two products are chemically compatible and the coating locks the sealant edges down. Keep the roller off the MaxxFan Deluxe lid itself (mask it with tape) and off the skylight dome, but coat fully up to their perimeter edges. Once cured, the roof should show a uniform matte surface with no visible color variation between old and new sealant — any remaining light spots mean thin coverage and need a third coat in that area. Plan to repeat this full inspection-and-coating cycle every two years.

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