We make reservations and while there are some places we won't fit, we find plenty of nice places to go where we do fit (we're "only" 34ft). We like to camp at state parks.... which are great, but some have "too many trees" (is that really a thing??). The one time we've been unable to back into a space due to tree placement around the driveways, the camp host found us a new spot (which we could pull through, which was great!).
So - plan ahead, check out photo galleries and google "satellite" or "earth" views, get reservations, and you should be good.