If you desire a seamless cup for continual use, as opposed to intermittent "survival" use, there are two options - 1)Stainless steel cups, preferably with folding handles, that fit snugly over the base of a Nalgene canteen - 2) titanium cups like the Snow Peak 700 - similar configuration and very tough and as light as aluminum. Titanium does not alter the taste of that nice cup of tea or whatever else you prepare in it. They are not cheap ($25+/-), but they will last forever.
Geezer in Chief