Suggest you buy or borrow a DC Clamp-on meter. I paid $70 for mine (Extech brand) at Northern Tool. Until you know how much you use, how can you determine how much you need to put back?
Where do you live, what time of year do you camp (all year?), blah blah?
Tioga George (Google his website) is one of the many who are successfully using a solar setup.
I love Camping World, but it would be one of the last places I'd buy solar panels. If you are paying more than about $5 per Watt, you can get a better deal with little shopping.