I have a 20' Haulmark with bench, cabinets, tire racks, etc. It is 3800 lbs empty. I installed a generator and compressor. My car is 2850 lbs and I carry two additional sets of wheels/tires, jack and stands, some brake rotors, tool box, and miscellaneous parts to the track.
I tow it with a 2000 Navigator 4x4 (tow package, self-leveling, posi, every option) a 1,000 lb weight distribution hitch, etc and it is unsafe at any speed! Tow capacity is rated 8200 lbs and I am pretty sure I am right there. It wanders like a pig just trying to go straight. When anything passes at a higher rate of speed it jumps out of its lane from the aero push. When going past a truck or bus, it pushes you sideways like crazy (think holding the wheel at a 45 degree angle just to stay going straight, and then when your front end just gets past the front of the truck/buses front end, quickly correcting to keep from driving into the truck!). The trailer drives the Navigator, you are just in there trying to stay out in front of the trailer. Don't do it!
Go get a cheap used long wheelbase pickup for towing, with gas at $4 + per gallon, I'll bet you could pick up a nice crew cab for not much more than how much the cost of the gas in it is. Oh yeah, I get 7-8 mpg when towing, and it is all freeway miles.
Seriously, don't pull a 20' + enclosed trailer carrying a Viper with a Navigator.
Sorry to the seller, I'm not trying to push away a buyer, in fact I sent this to a friend of mine who is looking for a 20-24' trailer, but it is so not fun towing my car I felt it wrong not to inform the guy with the Navigator.