electricity at the campsite

lots of way to do this, if you treat the trailer like a tent with a stove and use very little power, you could get away with no power and a couple good batteries.  My forst trailer was a 28 foot and we were very stingy on power.  with for 6V batteries I could easily got for 2 weeks in the summer, but all we would use for power is the lights in the camper pretty much.  when I got my 5th wheel I got solar put on and transfered the 6V batteries from the camper to it and now I never have to worry about power, but I don't use the AC and I still watch my power usage limiting the kids to 1 movie a night and I use the keurig in the morning and after supper, and limited microwave of 10 min a day.  this also includes the furnace in the fall.  

now if you have a 12V only fridge that adds another factor as they require battery power so a good battery bank is going to be essential

so you have options, and they depend on your power usage and what you want to run.  if you want to run the ac either get power where you camp of get a generator (I hate generators, but cost wise it is the cheepest option when your talking about AC usage), but you have to watch for rules goverening generator usage.  up here you get 2 hours in the morning and two hours around supper, and that is shrinking every year in atempts to phase them out.  If you can live with out the AC then solar is a exelant choice,   if you are a handy guy and you can install it your self you can have a awsome setup for under 600 bucks plus the cost of your batteries, but you should get good batteries no matter which way you go.