I had been planning on flanging panels and soldering my fuel tank together, like they used to do with vintage cars. However, this aircraft builder page
http://bobhooversblog.blogspot.com/2006 ... -tank.html has detailed information on building a riveted (aluminum or steel) tank using PVA sealer, which is supposed to be resistant to fuel, alcohol, or water. I still need to follow up to make sure the sealer is resistant against the nasties found in common pump gas - both methyl and ethyl alcohol, MTBE and ETBE, MMT, and so forth.
I've never had much luck with any of the old-gas-tank sealers, which always seemed to come off in flakes after a while, but I'm willing to consider there's a difference between sticking to rusty once-galvanized steel and clean etched aluminum. Might be worth an experiment, come to think of it...
more riveted tank pages:
http://www.krnet.org/wingtank/index.htmhttp://www.rvten.com/wings6.asphttp://www.my9a.com/wings6.asp