Yes you can disconnect battery without hurting a thing.
No, you won't hurt the battery by having it hooked to a maintainer.
More importantly, figure out the issue because it's likely not normal.
How many batteries does the rig have?
Are you talking about the start battery, house battery(s) or both?
If it has multiple batteries, is the start battery hooked to the house for charging? Could be the RV draining it, as the "truck" shouldn't.
Bottom line, just hooking a charger to it or disconnecting the battery doesn't fix the problem, it just puts it off.