Batteries should certainly last longer than a year. I pay a little extra for maintenance free batteries for a couple of reasons including checking them in my Lance TC is a PITA and the battery in the TT is big (a 4D which is equivalent to two group 27's).
First question is shy do you leave it plugged in? Second question is what model converter/charger is in the TT and is it a 3 way?
I would disconnect the battery in any case if you go for long periods without using the TT. If you don't have a built-in battery disconnect switch it's easy enough to add one right in the battery box. Check with your local RV store.
'09 Pacific Coachworks Tango 276RBS
95 Lance 880 Truck Camper
'91 F350 Dually 2WD CC 7.5L (76K Original miles!)
AirLift Bags, Reese Titan hitch, Rancho 9000X