To my knowledge, it''s not that you *should* avoid stainless but rather understand its liabilities. Your choices would seem to be:
1. Aluminum: subject to corrosion (dissimilar metals and water, especially from the inside)
2. Stainless: heavier, similar corrosion issues, usually not built up in the much preferred 316L/317L alloy
3. Fiberglass: perhaps the best choice but boats usually need to be designed with this in mind
4. Polyethylene (the XLPE type) which is either rotomolded or welded up, usually expensive since it is likely to be a one-off tank.
In all cases, how the tank is sited is very important - plastic tanks expand and can be chafed by what holds them in place, metal tanks can''t be exposed for extended periods to water so e.g. can''t rest directly on wood frames or supports, and so on.
Calder does a nice job on discussing all this in his Cruising Handbook.
FWIW I recently pulled out a 23 yr old aluminum tank and replaced it with an exact duplicate, also in aluminum. I chose this because the first one was in good shape after 23 years, I didn''t want the added weight of stainless, the metal shop was adamant about avoiding stainless in the alloys I could afford (he works to ABYC standards), and what''s available from other vendors was limited.