Should I make reservations or wing it?

RVing without reservations across country requires what Mark Twain called "A high level of tolerance for Ambiguity". Making and planning with reservations is not the same as getting married, having open heart surgery or having kids, reservations can be cancelled or changed with a simple phone call. You have everything to gain and nothing to lose by making reservations for your RV trip. When making reservations, always as what the RV parks cancellation policy is.