If it is going to sit for over a couple of days you need to use a battery disconnect switch to totally disconnect either POS or NEG battery terminal... The trailer has several what is called PARASITIC DRAINs that are connected at all times like the Propane ALARM sensors, maybe fridge or heater sense boards etc...
You can hook up a small output SOLAR Panel, BATTERY TENDER or just plug your trailer into a 120VAC Garage 15AMP power connection and allow the on-board converter/charger to keep your battery charged up.
I keep my trailer plugged into the garage connection all the time here when not on the road.
Been doing this since 2008 and batteries are still going.
Roy Ken