It comes down to either booking WAY in advance or waiting for last minute cancellations. I know that it can be frustrating.

We are here now for 18 days. Booked a 4 day reservation and kept grabbing 2 or three days here and there within the Maricopa County system, as other people canceled. It’s a lot of take down and set back up, but that’s what keeps us limber.

it's a really busy and popular place - my understanding is to get in even if it's one night, and move to different spots as they free up until you can reserve for a longer period.