agree, the 100 watt setup is a great starting point. It helps keep from running the battery down quickly.
Its good for putting "Something" back in the battery. Great for charging phones, will take the "Parasitic Draw" off the batteries or battery when producing solar.
I started with a 100 watt panel, went "dry camping" and it helped allot, after three days of battery use (heater at night and water pump) I would need to run my generator at dinner time to re charge the batts. But during the day I could run the heater, charge phones and play the on board radio.
Installed another 100 watt for 200 watts total and now we can go out for about five to six days before the need to run the generator.
We camp at the coast often so sometimes there is clear sky's and we get full solar, sometimes we don't but at least it still puts something back in!