Well that took a while.
Previously, I had fitted the front and back panels, and cut the rear window area of the front panel to match the back of the cab.
Wednesday night I cut a hole to crawl through in the back panel. I matched up the sides and did a final trim so they fit down to the top corners of the back panel, and installed side base boards, which are 5/8 plywood about 2" wide, and beveled to match the angle of the side panels. Then I screwed the sides to the base boards and the end panels.
I used pieces of strapping on the inside , leaving it proud of the curve. These got screwed on at about 5" intervals, then I used the power planer to trim them back down to the curve, mostly with the tops horizontal athwartships.
I set the top panel on, marked where it met the sides with a pencil, pulled it off, and cut off most of the excess. I don't want to cut off to much, so I left a little extra, and after screwing it down I went after it with the belt sander. It's still not perfect, but not bad, and I can still adjust it.
Aft of the back panel I added a few more blocks to connect the sides and tops and screwed them together.
I drilled 1 1/2" holes in the sides, just above the base boards, and a couple more holes in the aluminum sides of the flatbed where I can hook ratchet straps. The straps go side to side and are almost down at bed platform level. To take the assembly off, I loosen and remove the straps, and lift the cap so the front and back panel stakes come out of the stake pockets. There are a few blocks screwed to the bed to prevent the side base boards from moving inward as the ratchets are tightened.
I gave it one coat of a clear soak-in latex sealer, and I should give it a second coat. I'm debating front and back plexiglass, which I have in stock if needed. A ribbon over the rear hatch tended slightly inward while driving today.
So here are pictures from yesterday. I got some good stares from passers-by, watching from a window seat in a restaurant.
I shouldn't have shone my flashlight on the strap while taking that last one, and I need to clear out some sawdust and planer shavings from the construction process, but it seems successful.
No data yet, but it feels good. It's not a great beauty, but it's as least as good as some of the coroplast projects around here. I need to sand the top seams a little more, and then maybe some Zip Tape over them. Zip Tape is designed for sealing plywood sheathing seams on houses being built. I think those seams need protection and I don't feel like fussing with fiberglass and resin.
Edit to add: I stuck a 2 1/2" spot mirror on the lower inboard corner of the passenger side mirror. That should help a lot. For the driver's side, my neck turns well.