I have used trailers, both open flat and enclosed to haul my cars on/in for the past 20 years. I went through a couple of small, 16/18 ft. light trailers until I got smart and bought a 25 ft, 12,000 lb rated enclosed trailer, four wheel brakes, 8 lug wheels and an equalizer hitch.
A 25 ft trailer might sound a little long to most people, but believe me, once you have a good trailer the size raises to the occasion. An average 40/50 car will fit in a 20' trailer without to much trouble, however, keeping the tongue weight down might prove to be a challenge.. When towing, the tongue weight is all important.
Last May I hauled 7,500 lbs of building materials to my daughters new house in McCall, ID, a distance of 1,050 miles, I left there and then drove west 350 miles to Idaho Falls, ID to pick up a '52 Buick Riveria HT that I had purchased. The round trip was 2,200 miles in eight days. My tow vehicle is a F250 4 x 4 7.3 Diesel Super Duty.
Look around before you jump into the market for a trailer, the old adage, if a deal sounds to good to be true, it usually is. The enclosed trail I have cost $12,k when new, I bought it when it was four years old for $5k, it would still sell for at least $5k in a heart beat..
If you would like to PM me I will be glad to respond to any questions you have..