I have had some experience with solar and must say in this case more is better. I had a full solar/inverter setup on my 77 31 ft Soverign and it was wonderful!
Once you get hooked on free power and not hearing the HUM of the converter you will never look at boondocking the same again.
The idea of a battery keeper panel on the LP Bottle cover is good, but you need to consider your amps per hour rating. This is the amount of power the panel will produce in FULL sun. Based on where you store your rig and the position relative to the sun, you may not get the benifit you are looking for.
From a hookup standpoint if you put the panel on the bottle cover I would go to camping world and just get a new pigtail end, follow the wiring diagram in the owners manual and hook up to the charge line and ground from your tow vehicle inputs. Then you have a unit that you can eaisly mount and dismount without any holes for wires.
Just my 2 cents worth.