March would be a fairly busy time for Sedona because all the Phoenix-area snowbirders are heading north. That said, it's not impossible to get a site - unreserved.
I'm quite sure you could get one at Dead Horse Ranch State Park in nearby Cottonwood. They have plenty of sites It's an easy scenic drive to Sedona and it's very convenient to visit many other places such as Jerome and Prescott. We love that park! It has big spaces and electric but not sewer. They do have dump station.
Full-timed for 16 Years
. . . Back in S&B Again
Traveled in a 2004 Newmar Dutch Star 40' Diesel