I had the same issues in storing my coach in a garage in that after two weeks the chassis batteries would be low. There is no electric to the garage!
In the proccess of installing 400W of solar on the coach I added 2 50W panels, 1 on the roof of the RV and 1 on the roof of the garage. The systrm reguired a new charge controller and wiring for the added solar panels, 3 100W & 1 50W.
I disconnected the exsisting 100W panel and tied it into the new system to the coach battery bank giving me 400W's for dry camping.
I installed quick disconnects between the 50W panels wiring to the controller for factory system that came with the coach using the installed RV45D controller. Now when we are on the road I have the 50W panel on the coach connected and when the coach is stored the 50W panel on the roof of the garage is connected.
No more low batteries!!
Mark Bryant
06 Monterey 38