We do long distance travel also. Just about every year we have done a few months on the road and we usually play it by ear. I never make reservations before hand but call ahead the morning before or check on line when we are ready to move on. It just makes life so much easier. We have no issue with dry camping or boondocking so we have more places to stay than those who require electricity, I don't recommend WalMart or parking lots either. Not my idea of camping.
We try to stay under 200 miles on our travel day so we can leave late and arrive early.
Our first choice are public campgrounds, Military National, State or County but on occasion we will will stay at a private one to do laundry.