Pick up toppers, or canopies, are one of the most useful accessories available for a pickup. They allow you to cover and secure items in the back of the truck, but are generally set up for quick removal when an unobstructed bed is required. When installing, or reinstalling a pick up topper it is important to make sure the seal is good and won't leak. Almost all leaks in pickup toppers occur where the topper meets the truck bed.
Locate the leak in an installed topper. Mark the location, then remove the topper in order to inspect and repair the seal.
Inspect the topper and edge of the pickup bed for anything protruding which would keep the topper from sitting firmly on the truck bed. Old foam tape is often a culprit. Scrape, wash, or remove anything that might keep the topper from compressing the seal. Many newer pickups have a heavy rubber seal built into the bottom of the topper edge. Inspect the heavy seal for rips, cracks, or any sticks, rocks, or other debris that could inhibit a good seal.
Install the foam tape along the edge of the truck, sticky side down. Set the topper on the bed of the truck. Do not slide the topper on the tape. Sliding will cause the tape to tear, and you will get leaks at the tear locations. You must actually pick it up and set it down.
Re-inspect the seal once the topper is set in place. From inside the truck bed, look for any visible daylight. Lift and place foam tape into any visible openings.
Bolt or clamp the topper in place.
Always have help when removing or installing a pickup topper. Even light weight toppers are heavy and awkward for one person to handle on their own. In the case of fibreglass toppers you may need two or three helpers. Generally the foam tape rolls are labelled specifically for sealing pickup toppers, and one roll is the correct amount for sealing one pickup topper.
After working on the topper, and before driving, always make sure the topper is securely bolted or clamped to the truck bed.