It's nice to exercise them, but it's not a must. Look at all of the MHs stored in the northern states where it's way too cold to start them for 4 - 5 months. We store ours in AZ for 4 - 6 months at a time.
What is more important is having a true complete battery disconnect as Genecop does or else disconnect your battery terminals to make sure nothing is putting a parasitic draw on the batteries while you're gone. Nothing like getting off a plane to pick up the MH and having to deal with dead batteries.
Bill
Nodwell RN110 out moose hunting. 4-53 Detroit, Clark 5 spd, 40" wide tracks, 10:00x20 tires, 16,000# capacity, 22,000# weight. You know the mud is getting deep when it's coming in the doors.