Part of that years back was because there was no registration designation for "Dune Buggy" until ten years ago. Heck, when I registered my first dune buggy in 1967 I actually drove to the nearby DMV office and asked the officer in charge what I should do (showing him photos of my car and magazine pictures of buggies in California). He scratched his head for a while and then asked, "Is there some way that you could include sleeping or cooking facilities in that thing? If you could, you could register it as a camper."
So I bought a one-burner Coleman propane camp stove, secured it fast to the rear seat area (sharing the area with my 15.5 gallon aluminum Beer Keg gas tank), installed a dead propane cylinder in it (for looks) and registered it as a camper. Never got a blink out of anyone when I got the yearly inspection, either, and never failed an inspection.
I got stopped once by a DMV officer who read my registration and never even blinked - all he cared about was too much rear tire showing when viewed from behind. I ended up installing a round-the-back mudflap about 6" tall and that satisfied him. It actually made the car look better, too!