The rear section is made out of a pair of fenders from a mid 80's dodge caravan, we cut the shape out of the bottom. Then we added about a 3 inch strip down the middle. As far as mounting the seat we trimmed some of the original seat pan off and welded the tail to it, the best part about this is that the entire tail section comes off like the seat did. The only from modification we had to do was we cut a notch on the outside of each extension and bent them in a little.
The other nice thing about it is we welded a bottom onton the tail and put a hinged cover on the back of the seat, it you unbutton the back of the seat and you have a really nice storage area.
[attachment=696:0806101859.jpg]this kind of shows how it was put together, I will try to find some more detailed pics.