I had the same problem (corrosion) on the aft end of the tank on our 37. Our hole, however, was much smaller, 1/16" or so. As we were (are) broke, and it was winter and were using the tank for our Espar, we pulled it, peened and cleaned it, filled the hole from the inside with the "fuel" version of plumber's putty, then applied two tubes worth of JB Weld to the outside. Been fine for eight months, I'd expect to get a year or two out of it.
As you mentioned, that probably wouldn't work with a large hole, but it should not be a problem for a competent welder/tank shop to put a new bottom plate in.
There's alot of debate about aluminum vs. fiberglass tanks and corrosion. My personal opine is that a properly coated aluminum tank is fine. Key being properly. If you can find a super hard and durable epoxy like coal tar epoxy, that will give good protection in the bilge area and is very resistant to chipping, rubbing, scratches during install, etc., which is what causes most of the coated aluminum tanks to develop a local corrosion cell.
S/V ARGO - Pacific Seacraft 37 Hull No. 309