I have a battery disconnect on my truck because I rarely drive it and it would discharge the batteries (it didn't discharge the near as fast batteries until I put the trailer brake controller in so I know part of the cause). A trickle charger will help, but they have a tendency to declare a fault after a few days and stop charging: leaving you with a dead battery anyway. Still a trickle charger is a good idea as batteries don't like being discharged, just remember to check on it every few days. It is possible the draw is larger than the trickle charger can provide and that is why it doesn't work - I wouldn't know.
I have a JNC660 jump starter battery pack which I keep warm in the house. Others tell me this is the way to go (I just bought it so I can't say how it works). Some li-ion battery packs have a jump starter function - I have mixed results with them (It worked for me once, the next time I got a good crank but it cut out before the engine started).