There are two popular options;
Marine Goop, Or wet-install..
http://www.bigwatersedge.com/bwevb/s...ead.php?t=6508
As for the battery, Fry's sells a lot of different 12 volts, good prices. buy a waterproof battery box from oex, or make one from the $8 waterproof box/case that walmart sells in the camping section. 15 ah sounds like overkill. I have run my FF on 8 AA batteries for 1+ trips..