didn't get into the steel specs as it doesn't matter as long as no one is shooting at you, just normal mild steel plate is perfect, prep time along the weld seam isn't enough to worry about. just turn the amps up and go for it.
make no mistake though i am no master fabricator, just a guy that likes tanks. so don't take my word as gospel but it isn't rocket science either and when these things were put together in the factory 70 years ago they didn't do every weld perfectly !