How to Make a Tonneau Covers
Tonneau covers aren't particularly complicated, but they can make an enormous difference in the way a truck looks and performs. A well-designed tonneau cover will smooth a truck's aerodynamic profile and keep items in the bed secure, and look good doing it. Pickup trucks come in all different lengths and widths, with several configurations possible for any given chassis. Making your own DIY tonneau cover is a straightforward proposition, but does require some fairly advanced bodyworking skill to do right.
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Things You'll Need
- Two-by-four pressure-treated lumber
- Subfloor construction adhesive
- Screws
- Corner brackets
- 3/4-inch pressure-treated plywood
- Router and bits
- Dual-action sander and sandpaper
- Fiberglass resin and fiberglassing supplies
- Sanding board and sandpaper
- Primer
- Paint
- Piano hinge
- Barrel lock
- Cable
Instructions
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Build a framework of 2-by-4-inch lumber around your truck beds rails, laying the wood flat so that it hangs over the inside of the bed, and keeping the lumber flush with the character lines on top of the bed. Use construction adhesive to secure the edges of the two-by-fours to each other, and use inside corner brackets and screws to keep them together while the glue sets.
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Install a two-by-four cross-member in the center of your frame, just above the wheels, gluing the ends and using corner brackets to hold it in place. Coat the top of your two-by-four framework and cross-member with construction adhesive, and carefully lay a piece of 3/4-inch plywood on top of the framework. Drive a number of 1-inch countersunk screws into the wood to secure it to the framework.
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Remove the tonneau cover from your truck and take it somewhere that you can work on it with the router. Flip the tonneau cover over so the framework faces up. Fit a 45-degree cutter bit into your router and set the router guide to cut a 3/4-inch deep bevel. Run the router down the outer edge of one of your long two-by-fours, cutting the corner off to make room for your hinge. The bevel needs to be a bit larger than the hinge to leave room for fiberglass.
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Flip the tonneau cover back over. Reset the router guide to cut one inch deep. Use a circular saw to trim the edges off of the plywood if it protrudes past the frame; a perfectly straight edge is crucial here, so take your time.
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Run the router all the way around the edges of the tonneau cover to create a neatly beveled edge. You might also consider cutting in a few shallow, lengthwise grooves into the top of the top of the cover for decorative purposes and to channel water off of the cover.
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Fit some 180-grit sandpaper to a dual-action sander and sand the entire tonneau cover to as smooth as you can get it. Follow up with 500-grit sandpaper.
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Mix up some fiberglass resin according to the package directions, and thin it down slightly with some acetone. Apply the fiberglass resin and glass weave to the tonneau cover top, sides and bottom to fully seal it. Allow it to set up and apply a second and third coat of resin and fiberglass to form a protective shell around the wood. If you don't already know how to work fiberglass, then enlist the help of someone who does.
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Smooth the fiberglass completely smooth using a 3-foot-long sanding board and 180-grit, 500-grit and 1000-grit sandpaper. From here on out it's standard bodywork stuff; apply body filler, sand it flat, apply gap-filling primer, get it smooth and paint the tonneau cover. You might consider coating the bottom of the tonneau with truck bed coating for aesthetics and sound deadening.
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Screw the piano hinge to the bottom of the tonneau cover, then attach the piano hinge to the side of your bed. Apply some adhesive-backed, foam-core weatherstripping to the tops of the bed rails. At this point, you may opt to drill a hole in the top of the tonneau cover and through the bed rails to install a barrel-type security lock. Install a plastic-coated cable inside the tonneau cover to connect it to the bed rail and keep the cover from flopping all the way open and hitting the side of your truck.
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Tips & Warnings
While making a tonneau cover out of wood may seem a little silly, it's worth remembering that boat-makers have been using this construction method for a century. Fiberglass-coated wood is very strong and weatherproof -- you should be able to stand on the cover when you're done -- and starting out with wood will allow you to perfectly shape the tonneau cover to your truck before committing to fiberglass. The tonneau cover will end up fairly heavy -- probably in excess of 100 pounds on a large-bed truck -- but the side-hinge mounting method will keep it easy to lift and lower. Besides, trucks are engineered to carry extra weight over the rear axle, so a bit more mass here will help to enhance traction and stability.
