I studied my butt off when I purchased my trailer. I listened to guys who have been hauling for a while, those who have show cars, guys who have cars that they race, etc. I went with an H&H trailer 24' V-nose. It has plenty of room and it is enough trailer to handle more than I have currently. I have room for a couch (you have to have a place to drink beer at the track when it is raining) and it is wide enough for me to open the door over the top of the wheel well and step right out of the car. If you have a post car with a window frame, you will have to deal with how to get out. Things on the must list: 10,000# axles (greasable hubs are not a must), 48" curbside door, brakes on both axles (even if you go with a open trailer!), one piece roof, lights inside (even if it is just one in front and one at the back door), and 3/4" plywood floors.
Bonus goodies: LED lights, rivetless sides, camper style latch for the curb door, e-track in the floor, 7K drop leg jack.
Get a spare tire, get a weight distribution hitch, sway control is a nice option, and get a good brake controller. Cover your tires up to prevent UV rays from destroying the trailer tires. Anything else?
