It does sound like you need more than 200 watts if you're depleting your group 31s in one night. But like you said you have the generator to fall back on in worst case situations.
Solarblvd sent me email w/ black Friday sale of $1 watt 12 volt panels. 100 watt for $100. etc. If I was in your shoes and on a budget I'd start with 300W and build the system with expansion capability (maximize empty roof area, wiring, etc...
Do you typically park in full sun when camped?
Also in conjunction with this, I'd be certain my converter/charger is capable of 14.4 plus volts in first stage of battery charging.
Also as you probably know, keep eye on demand end. LEDs, reduced furnace time by using more blankets at night, lower idle loads such as inverter, possibly more efficient CPAP, low draw electronics, laptop, etc...
