Steve,
2 things.
1. you might consult pianotuna on this board(i think that's his moniker)-i've found that he's the most knowledgeable on this board about batteries and solar-he'runs practically everything with this.
2. even if you get 2 more batteries-your other charging methods won't be changing. the solar you have helps of course but you'll still be using the standard roadtrek alternator-you' wont have the 'engine generator super alternator' whatever.
your only bulk charging options will be plug in,generator,or standard
alternator.
if you won't(or can't) use the generator what do you have left.
you can plug in before you leave on a trip and be full. driving will help-but if you wan't to do extensive boondocking i see no option not to use the generator.
