Re: What to seal my new transom wood with? (other than epoxy)
You could just use marine plywood (if you can find it), uncoated. Or use pressure-treated and insulate it from the aluminum (roofing paper?).
I know you don't want to order the stuff and would prefer a local vendor, but I'm pretty happy with my US Composites epoxy. Buy a gallon and the pumps for $70, and be done w/ it. Any do-it-yourselfer will find a use for this stuff all over the house, plus you might need it for your next boat. I keep a stack of paper bowls and a box of Harbor Freight $0.10 chip brushes next to it.