i've recycled bus seat foam in 3 skoolies now. It's pretty nice foam actually. I just build a simple frame out of steel or 2x4's depending on how frisky i'm feeling. Then i cover the frame and the foam with pretty fabric. I make it tall enough to put a milk crate under the seat.
here are a couple examples:
this was my first bus...there is a couch in the foreground, and one of my recycled bus seat benches nearest to the glass block wall. I use bus seat "bottoms" for both the bottoms and the backs of hte seats.
here's bus 2
here is bus number 2 under construction