Lots of racing friends with stacker trailers. The two you see most in the paddock are Renegade and Gold Rush. Not the cheapest trailers, but very durable with high quality construction. You can find used trailers for sale in "Auto Week". Here's one of many websites you can go to for used car trailers
http://www.race-cars.com/trasales/complist.htm
Watch out for people who want to sell you steel framed stackers. They add a lot of weight and this cuts down on your road speed and fuel mileage.
I've used a 20' Haulmark for years since I only take one car to the track at a time. Several features I've added over time which are useful in any trailer:
1. A cradle for a large nitrogen bottle. Great for tire inflation and also handy to blow green and brown stuff out of the car when you go agricultural.
2. A cradle for my roll around tool box. Very stout. You don't want to think about one of these breaking loose in your trailer.
3. A workbench. Plywood and 2x4 construction with an aluminum work surface.
4. Cabinets. Lots of them. You can never take too much stuff with you to the track. Even if you don't use it, it might help one of your buddies get back on the track.
5. Fuel storage rack. I always haul 20 gallons of fuel with me to the track. I had two local fuel suppliers who always had good fuel. Track fuel can be iffy, and expensive.
6. Driver changing area. Once unloaded I have the center of the trailer set up with a fold down tray, mirror, and curtains. Put a lawn chair in there and it's a great place to lay on all that Nomex and clean yourself up after being on track. Also, kind of a private place to go to to get your head where it needs to be before strapping into the car.
7. Trailer spare tire. Too many ugly stories about guys who got a flat and had no spare.
8. Fan. Older formula cars with the radiators in the nose just roast the driver. I liked to have a fan to sit in front of after I got out of the car. Have only been on track in a Viper twice, but I can't recall if I got cooked.
9. Cameras. I have a small camera mounted above the rear door that diplays on a monitor in the RV cab. Grat for determining when you have cleared a passed vehicle. Thought about putting one inside the trailer also. Some guys do this for the peace of mind of knowing everything is okay, strapped down, and not burning.
10. Drip trays for the stacker. Cars that have been tracked just can't help themselves. They have to leak/vent. The bottom car can be a mess without drip trays above.
I talked with one of my stacker buddies. His input:
1. Positive(manual) Pin Locking. He likes to have four pins which he manually inserts to lock the upper ramp in place. Doesn't like automatic latching mechanisms.
2. Blocks. He keeps blocks in small racks on the wall for blocking newly rolled in cars. Paddocks aren't always level and he likes to have blocks at hand to hold a car in place until they can strap it in.
3. Ramp boards. He carries special boards that supplement the trailer ramps to help with clearance issues when loading cars, especially the one going on the upper ramp.
4. Distant Operation. He prefers to have an operator on a cord that gets them well away from the ramp when they are raising and lowering it. Most stackers come with a wall mounted operator that puts you close to the ramp as it goes up and down. A dropped car doesn't necessarily stay on the ramp.
5. Weigh it fully loaded. Run your trailer through a scale once you've got it crammed full of stuff including both cars. Make sure you are not exceeding the GVWR.
