We are "walmarters". Last 2 long trips were PA to FL and PA to TN and we used Walmart both times. Of course I am fine driving until midnight or longer, and at that point the kids are already asleep in the truck, so we are really just looking for a place to sleep. Find where the other RV's are, setup the generators, and hit the sack! My concern with making reservations along the way is I could see us getting to that spot and thinking "why did we stop, I could have made it 3 more hours". That said, if you have plenty of time and can take your time, totally different story. We have limited time off so we just want to get there.
