Kach,
Your situation can be made very simple - no need to make it more complex than necessary. Just wire your two 6V batteries in series as you say, using cable as heavy as automotive jumper cables along with the proper lead or brass battery connectors available at any automotive parts store.
If you don't need air conditioning, but want to both charge your batteries and operate a small (900 watts or less) microwave in your RV (plus small appliances such as a TV, computer, etc.) all you need is a quiet little 1000 watt generator - such as a Honda EU1000i. You can plug any 30 amp RV almost directly into the Honda's 120V AC receptacle using a simple 30 amp to 15 amp adapter that plugs onto the end of your RV's 30 amp hookup cable and then plugging the adapter into the Honda's connector. We ordered our adapter from Camping World for a few bucks to do this.
We just completed a 9 day dry camping trip (parked in the shade the whole time) with two Group 29 12V batteries wired in parallel (about equal in capacity to your two 6V golf cart batteries in series) using a tiny little ultra-quiet Honda EX650 (650 watt) generator to top up the batteries about every 3rd day. This little generator runs at full power almost as quiet (54dBA) as a Honda UE1000i does when it's idling (53dBA).
We do have a microwave in the RV and air conditioning - which we use a large built-in generator for whenever needed ... but this large generator is not needed at all for any of our battery charging. We consider it as a boondocking luxury item mainly useful when the DW wants to dry her hair or when we're camping in the extreme heat.
We could go many weeks (not counting the grey, black, and fresh water tank capacities) this way regardless of whether the sun is shining or not ... how long we can go depends upon how much EX650 fuel we carry and how much propane we carry.