Thanks Sen. Now that I've had more time to think about it and now have a friend who can weld aluminum, I'm going to cut the top tube out . I'll replace it with a straight tube and run two smaller tubes up from the seat post to the steer tube to outline a tank shape, and then weld in sides and a top plate to form the tank. More work, but that current top tube has to go.
I used krylon plastic paint for the side walls. Sprayed it into a cup and brushed it on in many thin coats. Next time I will order real white tire paint though.