Here is a related thread with build parts lists, photos, and conversation about PVC tube and end caps used to build MB fuel tanks.
http://motorbicycling.com/f3/pvc-tank-how-21154.html
There are different grades of plastic, and many fuel tanks are made of it, including the large square 5gallon pure alcohol cans for race track use.
PVC is not the same plastic, but has worked for a lot of people to make go cart, mb, and generator tanks.
I would like to see some pics.. I like the idea of a pvc tank. Cheap and easy.