I have not installed the system you describe; but I do have some observations based on the upgrade I did to my unit.
First, the easiest way to "increase" your battery capacity is to reduce your load. We changed over to LED interior lights - and removed some storage compartment lights so they could not be left on. Also, make sure that your refrigerator "anti-sweat" switch is turned off; it takes ALOT of electricity. (DAMHIKT).
Second you should consider upgrading to a "three stage"(?) smart charger - or whatever they are called. The older designs - Univolt - are much heavier and can cook your battery. I opted for a smaller charger - max 35 amps? - because batteries last longer if they are not rapidly charged - or so I have been told.
Third, you will want the batteries, charger and fuse panel close proximity; it makes wiring and trouble shooting easier. My current unit has two battery boxes up front with the charger under the sofa; I just had to add an extra battery and upgrade the charger as the wiring was already there. Batteries are heavy and you will need to service them.
Finally, there are lots of choices regarding battery types - you can search and find all sorts of opinions. I went with two standard size (24/27?) 12 volt
deep cycle marine batteries. They are readily available almost any where - not so sure about finding a golf cart battery on a weekend in a small town. I also set them up with a "4 way switch" so I can isolate each battery - or charge them together. It makes checking them simple - when I get down to about 12 volts I switch to the other one and plan my trip so I can get to shore power in about 3/4 days. It works for us.
Check the archives and see what everyone else has to say.