I'm leaving Seattle on May 25th and heading down the Pacific Coast to Phoenix. I'm traveling with a 16yr old and a medium sized dog.

I plan on camping during most of the trip (unless its raining). My question is: should I make reservations or just wing it?
I know there are good points and bad points for each. I don't think I'm traveling during a very busy time so if I wing it, I'm guessing I won't have a hard time finding a campsite or dog friendly hotel room.

Anyone have any opinions either way? Winging it is taking a chance, but making reservations you are committed to being at a certain place for a certain time.