Well, I hope the last post by OP was not entirely meant for me :)...
Sorry, I failed to see why you can't "match" two 120W panels. Did you mean matching them with each other? Or with this MPPT? MPPT will take N volts in and put nominal 12V out, be it parallel or series. There is no matching issues here, unless your two 120W are way too different from each other.
With MPPT controller you would benefit more by wiring 12V panels in series though. In parallel there will be too little difference between input and output voltage for MPPT to work.
IMO, camper should have enough roof for 3*120W. They are - usually - 5ft by 2 ft each. Or - 3*100W.
