Always start tracking down current draw problems from the batteries and work to the potental draws. Start by removing the cable to your battery bank and check for dirty or corroded terminals in all ground wires and connections and if any are found repair. Then ,check all positive connections and tighten and clean. Next, connect an amp meter in series with the + battery terminal and cable. Remove all fuses or power draw circuits not fused. Make sure there is no current draw. If there is a draw with everything disconnected, your short is in the wireing between the battery and the fuse block or through the ground circuit. If no draw is found, start by inserting fuses back one at a time to see current draws. Most refers will have a parasitic draw through thier circuits as well as TVs, anything with a pilot light, digital displays, smoke and lp detectors, chargers and even some electric water heaters. Add up the draws from all circuits and you may find with all circuits connected the parasitic draw will be as high as 5 amps. More then enough to drain 2 batteries in 2-3 weeks.
Add a battery dissconect switch to isolate your battery bank from parasitic draws when stored.
Good luck,
-Paul R. Haller-