ESI Super Cap Seal XL EPDM truck cap seal 2 1/8" x 1/2" x 20' — heavy-duty, weather-resistant for caps over 200 lb

ESI Super Cap Seal XL 20 FT is a 2 1/8" x 1/2" EPDM rubber seal kit designed to mount heavy truck caps or camper shells on extra-wide bed rails, delivering a durable, weather-resistant barrier for caps over 200 lbs.

If you’re fitting a camper shell or truck cap that sits on wide bed rails and weighs more than 200 pounds, the Super Cap Seal XL provides a professional-grade, long-lasting seal. This kit includes 20 feet of automotive EPDM rubber seal sized for larger rails, plus butyl tape, alcohol wipes and clear instructions so you can trim and install the seal to match your truck’s exact rail dimensions. Made in the USA and engineered for installers who want a better alternative to PVC or foam, this seal resists compression set and absorbs vibration so you don’t need to swap it every time the cap is removed.

How do I know if the Super Cap Seal XL fits my truck cap and bed rails?

Measure the gap between the cap’s base rail and your truck’s front bed rail (include any bed rail caps). If the height difference is .250 inches or less, the Super Cap Seal XL alone is appropriate. Larger gaps require combining this seal with a Front Rail Seal or Front Rail Seal XL depending on the gap size.

• Gap ≤ 0.250": install Super Cap Seal XL only
• Gap .251"–.487": add Front Rail Seal on cap front base rail, use Super Cap Seal XL on side rails
• Gap .488"–.875": use Super Cap Seal XL on front and side base rails plus Front Rail Seal XL on truck front rail
• For 8' beds that need over 20' of seal, the 23' Super Cap Seal XL variant is available (ASIN included on pack)

What materials and performance can I expect from this seal kit?

The Super Cap Seal XL is manufactured from automotive-grade EPDM rubber chosen for weather resistance, elasticity and long service life. EPDM outperforms PVC and foam in resisting compression set, so the seal maintains shape under heavy caps and repeated removal. The kit is assembled for installer convenience and durability rather than a disposable product.

• Material: high-grade EPDM rubber for UV and ozone resistance
• Compression set resistance for long-term sealing and vibration damping
• Includes butyl tape and alcohol pads to ensure a reliable adhesive bond
• Made in the USA and preferred by professional installers

How easy is it to install and trim the Super Cap Seal XL?

Installation is straightforward: clean the rail surfaces with the included alcohol pads, cut the seal to fit, and use the supplied butyl tape to adhere the profile to the cap base rail. The profile is engineered to be trimmed to shorter widths so it fits trucks with narrower bed rails, and the kit contains step-by-step instructions suited for DIYers and pros alike.

• Includes detailed instructions, butyl tape and alcohol pads
• Seal trims easily to fit smaller front bed rails or nonstandard widths
• No special tools required beyond common cutting and measuring tools
• Designed so you don’t have to replace the seal each time the cap is removed

Will this seal hold up under heavy use and harsh weather?

Yes. The EPDM compound and robust profile were selected to withstand repeated compression, road vibration and environmental exposure. Users report it maintains a consistent seal through seasonal temperature changes and daily driving conditions without frequent replacement.

• Resists environmental degradation (sun, ozone, rain)
• Absorbs vibration from heavy caps to reduce noise and movement
• Maintains sealing force after repeated installs and removals
• Suitable for caps and shells exceeding 200 lbs

Who is this for: The ESI Super Cap Seal XL 20 FT is made for truck owners, aftermarket installers and professional cap shops fitting heavy camper shells or caps on extra-wide bed rails. It’s ideal if you need a reliable, long-lasting EPDM seal that trims to fit, comes with adhesive and prep materials, and is built to stay serviceable through multiple installations. If your bed is 8' and requires more than 20' of seal, consider the 23' model referenced on the packaging.