I have made a couple of tanks out of epoxy resin, fibreglass or dynel cloth and styrofoam. You shape the styrofoam to the desired shape of the tank, then lay up the cloth and resin on the foam plug. after the resin is cured, you cut a hole in the tank (e.g. for the sender) and pour gas into the tank. The gas dissolves the foam and you are left with a hollow tank. Make sure you use epoxy resin; polyester resin will eat the foam. You can make a tank to fit any application using this method. Don't forget to include baffles in the design.
Gord.
