As an HVAC contractor I do a lot of silver soldering. I've got some 45%, 15% and some 5% (econo solder jobs..
) on my truck. With a very thin wall brass tank it'll be somewhat difficult to control temps with the comparitively high melting point of silver solder. The thin brass tends to warp and buckle, sometimes even splitting. I can soft solder with 95/5 (tin antimony)which has a shear strength approaching siver solder's.
Dave