Based on my experience, I would not make reservations days in advance. We travelled for three months this summer, and would usually call ahead around noon to 1:00 the day we expected to arrive. We always got a spot this way. However, quite often when we'd arrive to check in around 5pm, others would be pulling in and there was no place for them.
I see that you're a Good Sam member. Go to their website and use the trip planner. It's a great tool for laying out your excursion.
If you get close to Tucson, send me a PM and I'll give you some great places to stay and some terrific attractions to see.