I've made a few tanks for old cars and old airplanes.
These are two non-welded stainless tanks that were pressure tested to 22psi.
Soldered lap-seam construction.
.040" stainless 304.
(No distortion from welding.)
(Thick stainless has less tendency to distort, so furniture and art stuff is made thick and welded.)
I am no expert, but I have made a few fuel tanks, oil tanks, water tanks.
(No leaks.)
1914 Packard tank, Browning, copy.jpg
1934 Packard tank,.jpg
(the owners of these two drove their restored Packards on 5000km x-country tours in Aus and US. I was asked to "build to last" - that's why the removable electric in-tank pump cover is seen on the 1934.)