That crazy nutter of Colin Furze is at it again with more garage tinkering, this time making 3D shapes out of completely flat metal sheets, using water pressure to inflate them like water balloons—a process called hydroforming.
I'd be scared to trust the welds to hold. Hydroforming was used in a Mythbusters episode for some ancient torpedo. They had solid forms to hold the sheets air tight and didn't run into folding problems. Of course they have much more equipment than most people. skip to 1:00