Loved the dunes at little Sahara in Oklahoma. Easy to get to, easy camping. Wish there were more bathrooms/showers.
The dunes were unbelievable, a different ride every morning as the sands shift at night. I was a novice, so after riding a few days with the pros, I was able to navigate the park myself. If you hit the parameter fence just follow it in to the camping...eventually.
People are friendly, you can ride to town on your bikes. Food and gas is right around the corner.