All great tips posted already...
At campgrounds, ask for a pull-through or if you have to back-in, ask cg personnel to help you or a NUMBER of campers will be more than happy to help you back in... LOL. Just remember, no matter "who" helps you, the responsibility to keep both eyes open for objects that are out to get ya,
is still yours. Check out overhead branches too!
I have backed in fivers or motorhomes by myself... just constantly on the lookout. Lots of practice and then more practice. Good Luck.