Do 12V devices currently operate in the TT? Do the interior lights turn on when its not plugged into shore power? If not, the battery is either completely dead or missing altogether. If missing altogether, that will just make your search that much more difficult because you'll be looking for orphaned wires instead of a battery!
Looks like Eh,Steve! might have just found them for you, though!
2012 Aspen Trail 2710BH | 280 watts of solar on the roof | 2x6V GC batteries | 100% LED lighting | 1500 & 300 watt PSW inverters | so far strictly boondocking