: Could you give a brief description on how you did it?

: I was planning on 3/4 plywood for the ribs and the cap rail. I want to find a
: door and windows off a wrecked shell. First step is to trace the cab
: outline and figure how to follow the back profile.

To start out: A DISCLAIMER:

I am not an engineer, nor have I ever played one on TV. I can’t, and don’t try to, distinguish between a safety factor multiplier and a modulus of elasticity. Every engineer who has seen this, including my oldest brother, has expressed shock and concern at its (apparent to them, anyway) flimsiness. I did what I did, but if anyone out there wants to crunch the numbers and proffer their criticisms, I’ll gladly cooperate as long as they agree to post the results, good or bad. It’s held up so far with no failure after 18 months. Well... , there was the accident, but that damage has been repaired. This canopy, or topper, is as strong as I felt I needed it to be: Carry two solo kayaks at freeway speeds in high winds, not flex on rough roads, and I can stand (and even bounce a little bit) even on the un-ribbed sections of the roof. Oh, and to keep the rain out when I want to sleep back there. I expect that in a rollover accident it would collapse, so if I had kids, they wouldn’t ride back there even if it was legal. I built the topper for my own personal use, so I’d get (and pay for) expert analysis if I seriously contemplated doing this for pay.

That said, this is what I did:

Much as you are contemplating, I started with .75” plywood strips laid on top of the two side rails of the truck bed. For my Ford stepside, this meant cutting curved slices that were flush on the inside; almost every other truck in the world will have straight sides. On the outside edge I made the plywood wide enough to overhang so that the cedar siding strips could continue down below the level of the rails to create a weatherproof overhanging overlap of about 1” held out about .5” away from the rail. On top of these rails I also made stiffeners of .75” plywood. These 2” high vertical pieces run atop the railpieces, flush on the outside. At the end of the project, I tacked on trim strips to the interior surfaces of the rail tops and their stiffeners.

The only large pattern I made was for the shape of the sides from the plywood rails up to the top of the curve, i.e., not including the roof itself. This pattern I freehanded and shaped, mostly following the shape of the rear of the cab until it looked right. I used cardboard until I got the final shape, then transferred this to a piece of .75 particle board for the ‘final’ pattern, which was duplicated a total of 13 times (I used it at last as one of the temporary forms).

Call the bulkhead at the front Station #1; this is .5” strand board with cedar strips as an interior decorative liner and holes cut to match the cab rear windows. The two side windows are ‘glazed’ with clear plastic, but the middle is open to allow use of the cab’s pass-through window. Stations #2 and #3, at about 1’ and 2’ aft of #1, were temporary forms consisting of particle board copied off the pattern, but for the roof I just tacked on scraps to hold them apart until I had all the forms in place and could see what I needed for a roof line. Then, I cut particle board pieces with a curve on top and screwed them to the forms, again, fussing until they looked right.

Station #4 is at about the middle (about 3' aft of #1), so I made a permanent rib of 1.25” cedar boards in 3 pieces much as I did the temporary forms except that they were made pretty. I kept the rib about 2” deep except at the bottom where it flares to meet the width of the rail tops.

Stations #5 and #6, about 4' and 5’ back from #1, were temporary forms just like #s 2 and 3.

Station #7 was made from a single piece of .5” strand board, like #1, but with the much larger opening for the rear. Its base is about 3” forward of the very end of the tail of the rails to allow for that much thickness of the rear panel (also to give the sill of the window piece something to rest on). Set flush with the rear ends of the side strips, I faced it with .75” cedar boards to make a ledge-like mating surface for the window piece. Later, a foam rubber gasket strip was mounted in there for weatherproofing

The sides are 1.5” x .25” clear cedar strips ripped out of a couple of 8’ 2 x 4s, then bookmatched, sort of. I used these from the bottom up to the top of the sides. Starting at a point where it can’t be seen from the side, I covered the roof with .25” luan plywood, cut into 6” wide pieces with cedar strips in between.

Everything, inside and out, was covered with a single layer of 6 oz. glass, a local brand of marine epoxy, and Epiphanes varnish. Some joints, e.g., the stiffener-to-railtop, are reinforced with deck screws. The whole thing is held onto the truck bed with conventional aluminum alloy clamps, about $5 each, from a local topper manufacturer. You need 4 for a short bed, 6 for a regular length bed. I used 4, but later recovered 2 from the scene of the accident, and the other 2 were broken.

This is the end of Part A. If you haven’t lapsed into a coma yet, go to Part B for another mini-lecture on the window piece.