What thickness aluminum are people TIG welding their custom pipes with?
I had a friend TIG weld .035" wall aluminum muffler sections to two of my pipes.
A pipe will surely see more stresses than a fuel tank.
You can MIG weld 1/8" aluminum.....
TIG is far more controllable and will produce better results every time over MIG . The .035 will likely crack depending on amount of filler rod used and support of the muffler .
Thomas , keep going with your project , depending on how much time you put on the tanks they may work for you . always good to experiment , much is learned .