I don't know that there's some kind of in line "filter" you could use with a regular generator. We bought a Honda EU 3000 i Handi four years ago to make sure we wouldn't damage anything in our RV.
If budget is your biggest concern I'd buy a small 1,000 watt inverter style generator so you have something to power your (small) electrical needs and still be safe to use. Other wise there's always renting a generator that you might take along for a temporary solution.
Another consideration, make sure the campground you're going to will allow the use of generators. Here in WI they are banned.
Dan
