which r-pod should I buy?

As for battery maintenance, what you read in the "manual" thread is what you need to do.  Lead acid batteries must stay charged or they will be damaged.  Just sitting there they slowly lose their charge so if you stick it on the shelf and walk away for 6 months it will be damaged.  Do that twice and it will be dead.

I suggest you get something called a Kill-A-Watt.  You can first use it around the house to see how much power your stuff uses - like your hair dryer.  You might find some things use more power than they should - often a fridge more than 10 years old is a great first test.  Then you can plug it into a visible outlet in the pod to keep an eye on the campground's voltage while you are in-camp.  In my 171 it's plugged into an outlet I see every time I enter so I see it often.  If the voltage goes below 110 volts (or above 130) you need to disconnect your pod to prevent damage to the A/C and possibly other components.  It should normally be around 120.

Congrats on your 178 purchase!  I like that one a lot.