flboy, Howdy;
Don, what ya have looks good. If I were doing this for my truck (8' bed with 2'+ gap tailgate,
I would, like you, go for 2 panels of ply 1 for top and 1 for bottom. For the track I'd prefer to
use some 'U" channel for the rollers (counter-sunk fasteners), so the wheels won't groove the
wood over time and usage. Spacing of the wheels is a personal thing. Me ... I'd go for every
12" and see how that works. Ya ain't haulin' an elephant back there are ya??? That 'L' stuff has
more backbone then most folks give it credit for.
Those are my thoughts and you're free to bend, twist or throw'em out if ya want.
Good luck with the project. Keep us oooo'in and ahhhh'in.
hank