I can easily cobble something together for my occasional (and light) loads. Square tube, cutoff saw, welder and a Saturday and all done. I was hoping there was an example floating around of something classy though, since my work tends to the utilitarian style . . . ;-P
As per Kevin's comment above: is it better to wrap the square tube uprights in wood where they go into the stake pockets? Or just steel on steel as snug a fit as one can go? I think the wood option would risk the least damage.
Probably make an upright frame for the front and rear of the bed that slide into the stake pockets, and then lateral pieces running fore and aft that can be quickly removed with cotter pins, and that should be enough for 100 lbs of 12-14' lumber even without cantilevered support over the cab.
