There have been occasions where someone gets a used fiberglass camper shell. For the most part the shell will fit the truck but there are instances where opening doesn’t match the truck’s rear window or is damaged. Here this thing, if you’re planning to use an accordion boot to connect the cab and the camper, you will run into problems
Here is why, The accordion boot only works if the two openings are the exact same outside perimeter measurement and shape . If they’re off, even by a little, the boot will twist, buckle, or leave gaps. That means it won’t seal properly and creates a faulty pass-through connection.
Luckily, there’s a fix. I found this video that does a good job of fixing the problem fabricating a new wall with fiberglass:
Why the Opening Matters
The accordion boot is a flexible gasket. It’s designed to fill the gap between two flat, parallel surfaces that have the same outline. If the camper shell’s opening is bigger, smaller, or shaped differently than the truck window, the boot will never seat correctly. Instead of sealing, it buckles, folds, or pulls away at the corners. The best fix is to modify the camper shell’s front wall. Unfortunately “close enough” will create installation headaches.
Here’s How to Do It
Step-by-Step Overview to create a fiberglass wall to receive accordion boot
Measure and Template
Measure your truck’s rear window opening precisely. Cut a cardboard template until it matches perfectly. This is your guide.
Frame the Gap
If the camper shell opening is too large, build up a support frame with plywood or foam inside the opening. Make the form larger to allow you to fine tune the opening with matching both openings
Prepare the surface
Using sandpaper sand the camper shell fiberglass in the are you are creating the new wall. This will help the new fiberglass bond
Apply Fiberglass
Apply resin, lay down fiberglass cloth, and roll out bubbles. Keep it flat and smooth. To create a bond overlap fiberglass to existing shell.
Create the right thickness
Add 2–3 layers (or more, depending on thickness). Let each cure properly. target the thickness to be about 1/8″
Trim and Finish
Allow the fiberglass to partially cure and use the utility knife to remove the excess. Once cured, trim with jigsaw or use a grinder on the edges to your template. Sand smooth.
Smooth Surface
If needed to smooth out surface use body filler to fill in dips. Note: the smoother and level the the fiberglass
Test Fit
Before final installation, test the boot against both sides to confirm alignment. Make any fine adjustments.
Tools
- tape measure
- utility knife
- saw/jigsaw
- rollers and brushes
- grinder
- safety gear (respirator, gloves, goggles).
Materials
- Fiberglass cloth or mat
- Polyester Resin and hardener
- Paint (to finish it)
- Body filler
- Something to create a form to apply fiberglass. Any flat thin panel can work. Plywood, foam board, Masonite
- Masking Tape
- sandpaper
Pro Tips
- Always scuff and sand surfaces before laying fiberglass—bonding depends on it.
- Ventilate your workspace. Resin fumes aren’t something you want to breathe.
- Double-check your perimeter measurement and size before glassing. Even a ¼ inch off can ruin the boot fit.
- It is better to have to much material than too litter because it is easier to remove fiberglass than to add more.
Why This Fix Works
By fabricating the front wall of your camper shell, you bring the opening into perfect alignment with your truck’s rear window. That allows the accordion boot to fit perfectly all the way around. No twisting, no gaps, no buckling.
Final Thoughts
If your shell opening and truck window don’t match, the boot won’t work—simple as that. But with a little fiberglass work, you can rebuild the shell’s front wall to match exactly. The video above walks through the process, and once you’ve done it, your accordion boot will seat like it should, giving you a clean, weatherproof pass-through.
Frequently Asked Questions
Why does the camper shell opening need to match the truck window?
The accordion boot only seals correctly when both openings are the same size and shape on the outside perimeter. If they don’t match, the boot will twist, buckle, or leave gaps that let in water, dust, and noise.
Can I make small adjustments to the accordion boot instead of fiberglass?
If the perimeter is off by more than a fraction of an inch you will have problems fitting the boot. Fiberglassing a new wall section ensures a solid, factory-style fit.
Do I need special tools to work with fiberglass?
Not really. You’ll need basics like a saw or jigsaw, rollers, brushes, mixing cups, and sandpaper. Safety gear is essential: a respirator, gloves, and goggles.
How many fiberglass layers should I use?
To get good results you will need about 2–4 layers of fiberglass cloth. For extra strength, especially on larger openings, you can add more layers.
What if my camper shell opening is larger than my truck window?
In that case, you’ll need to “shrink” the opening by building up the perimeter with fiberglass. The goal is to reshape the shell wall until it matches your truck’s rear window opening exactly.
Can I paint over the fiberglass when I’m done?
Yes. Once cured and sanded smooth, you can coat the fiberglass with paint for a factory look. For best results use primer and matching paint to blend it with your camper shell.
Rubber Boot Seal
You can order rubber boot material for your special project requiring pass through access. These seals are extruded from a durable EPDM synthetic rubber and incorporate a flexible spring steel clip for attachment to any flange. This material is sold by the foot. Choose between accordion boot or compression boot.
Resources
Here are some helpful links and references if you’re planning to modify your camper shell or work with fiberglass:
- West System: Fiberglass Boat Repair & Maintenance Guide – clear instructions on resin mixing, fiberglass cloth, and curing techniques.
- How to Work with Fiberglass – practical DIY tips for working with fiberglass materials.
- Truck Camper Magazine – Pass Through Windows Survey – insights into why truck camper owners use pass-throughs.
- Safety First! Working with Fiberglass and Resin Products – By following these simple tips, you can make safety a top priority while enjoying your fiberglass and resin projects.
- Repairing Fiberglass – Step by step instructions on doing fiberglass repairs.