Re: How to make custom gas tanks...
What about fiberglass tanks? I've built two metal tanks, only one of them worked out in the end and I'm still not happy with it. I'm not that great at welding, but I do know a thing or two about composites. Over the winter I plan to replace my crappy metal tank with a fiberglass one.
Since I haven't done it yet, I can't tell you much about making a tank out of this stuff other than- you must use epoxy resin. As I understand it, polyester is not resistant to gasoline.