I was so sick of not being able to run the furnace all night while Wallydocking, that I finally went out and bought two 6volt gold cart batteries to replace the one Excide deep cycle marine that came with the trailer. I ended up with two Deka GC25′s. Cost about $300 for the two, but so far with the testing I have done, we should be able to run for about 3-4 days with no trouble. Definitely worth the upgrade.
Heres the forum post about it all here.