Unless you have some way to charge the batteries, they will go flat in about 2-3 weeks, tops, if you don't use the on-board disconnect or otherwise physically disconnect them by pulling a cable. There are parasitic draws on the system, even if everything is turned off. Clocks on the microwave, TVs, DVD players, stereo, gas detectors and (if hardwired) smoke detectors all draw power all the time as long as there's power. I know on my Komfort, =everything= is killed with the house disconnect, except the slide and landing leg motors. FWIW, the disconnect on my FW also kills the battery charger, which I found out the hard way right before a boondocking trip.
Fully charged, they shouldn't freeze and should last several months without a problem.
Lyle