
The point of no return:

I took a few measurements off a real truck but nothing seemed to add up right, so I guessed and decided 1/4" behind the wheel opening and 3/4" before would be close enough. Then I cut some strips off a For Sale sign and stuck them on the back of the bed side to give some rough structure:

Then I chopped up some more For Sale sign and started filling the gaps. It's going to take a heck of a lot of putty but I think it might just work.












