Everytime we went (6 or 7 times) we stayed at slickrock campground.
http://www.slickrockcampground.com/reservations.html There wheeler friendly, and usually have propane onsite if your buggy runs on it. They don't seem too be picky about doing repairs on site also. Have built driveshafts, rebuilt front ends, replaced fuel tanks all in there park with no questions.
On the no tag buggy, If you have someone else coming out with a tagged vehicle, keep them behind you. If your rolling solo, DONT drive like a ****. If you do, they will pop you. If your nice and respectful, you should be fine. My Jeep and Yota both had tags, but no fenders and 42's so I was carefull. None of our club ever was hassled.
Go too Area BFE!
Potato salad hill is fun, and something you should hit, It isn't difficult but is pretty famous.
Rusty nail is a good trail, fairly difficult in spots. Its more fun running it backwards.
Be sure too pack food and water, some trails can take a long ass time too complete depending on trail traffic.
Any other questions, feel free too pm me.
The most important thing: Eat at Milts. Its a burger stand in town. Bacon cheese burgers