[dsraven]

I agree with LG, don't use plywood if you don't have to. do a trip to the local wrecker and see how the seats from modern vehicles are put together. some have a sheet metal frame where the upholstery attaches and the fabric has a plastic piece that is sort of folded over so it can hook on that sheet metal edge. some have an edge sewn into the fabric like a cording along tyhe edge and then hog rings can be used to slip through that and be attached to a spot on the metal frame that is made to hold the hog ring. if you take a tape measure you could look at some minivan bench seats from an astro van or maybe a rear seat from a yukon or something else that would be the width you need. that would get you a contoured foam cushion and a cover already made. you could grab some springs as well if you find some the right width etc or maybe grab the whole seat and fab a new base to fit your floor. some of the seats will even flip forward.