another option and i am serious about this.
If you know someone that works in the rotational molding plastics industry they can slap a motorcycle tank on a arm filled with a little crosslink plastic (resistant to gas) into the oven and give er a coat. I have heard of a guy doin this at my work before but I would prolly get canned if I tried. Apparently it works, his tank was pretty much new and all he had to do is cut out the holes for his gas lines and cap after. We made the buell tanks years back, and I know there are a lot of plastics companies thru the world, some of which may be able to help you for cheap.