If you could post a pic that would be very helpful. I have never heard of a fifth wheel that small, much less one with only a single axle, so I'm inclined to agree with the DMV that this is a home made rig. While it's true that truck campers don't need tags that's only because they ride in the truck bed. Generally speaking, anything with tires that rolls on the road needs tags.
Weekender is a brand of truck camper (
here's one) so the camper itself is factory made, what makes it a "home made" is taking a truck camper and converting it into a fifth wheel by putting an axle under it. Whoever had it probably didn't have the right truck to tote it around and by converting it to a 5er with a very light pin weight could pull it around with a small truck like a Ford Ranger.
