solar panel

You don't have to switch between batteries, just mount both and wire them in parallel.. It's IMHO the best and easiest option. You can switch to two 6v GC batteries, and wire them in series, that is the BEST option for boondocking.

The charger can be hooked up to them while in use. 40 watts is probably not going to be enough to stay at full capacity, but it should be enough to keep you out for an extended length of time, as long as you don't have a high battery drain day or night, like having to run the furnace. The furnace uses a lot of power to run it's fan.  It's the highest draw in the camper, other than the fridge on 12v, never run the fridge on 12v if not hooked up to the TV or shore power. We only run 12v when towing.

Lets say on a good day your solar charger can replace 50% of your capacity... probably a bit high in actual use, but just to get a feel for how it can work.. if you use less than 50% of your capacity on any one day, the charger will bring them back to 100%.. but if you used say 60%, then they are only going to bring you back to 90%.. but that is way better than the 40% you would have had with no charger.

Ok thanks guys. So if I hook up to batteries in line, do I just hook up the solar panel to one battery to recharge and that in turn will also charge the other batter? Like I said complete novice on this solar panel, dual hook up thing... I'd get someone with knowledge about inline batteries to be around when/if I go to hook them together...

I wired my solar charger directly into the charging input line from the bargemman connector and output from the charger side of the inverter/charger.  I put a standard recessed input connector (a male 120v wall mount) on the outer wall next to the 30 Amp input.  I labeled it "Solar Charger Input Only".   Then I Used a 25 foot ext cord - 14 ga to reduce voltage to connect to the output of the converted on the panels.  It works well, we just put it on a folding chair and manually track the sun.  We use a dual 6V system. I have some photos on the other forum last summer.