I have two 50AH batteries and an inverter in the tongue box of our trailer (
JonRocket.com Trailer by Roger Smith) which I use for recharging my P3P's batteries (as well as other things like running a fan on really hot Florida days). The battery setup works well (and is a lot quieter than a generator!). It works great for single-day adventures, but, even without a fan running, it runs out of juice after the first day. So, I bought the generator that I mentioned earlier for those longer periods of time when the batteries aren't enough.
I Included two 12V "cigarette lighter" plugs in my battery setup. So, I just bought a car adapter for charging my P3P batteries. If it works well, I might buy a couple more and use them instead of the AC adapters., As has been mentioned, they'll be more efficient than using the inverter and AC chargers. But, I'll probably leave the inverter turned on since I use it for other things and it acts as a low-voltage alarm for the batteries.