When I was looking at enclosed car trailers 5 years ago, I was thinking that a 20 footer would be more than adequate for my Fairmont, but after a lot of research, I bought a used 24 foot Wells Cargo. Its amazing how fast much of that "extra space" gets used up with the work bench, upper and lower cabinets, pit scooter, fuel jugs, floor jack and jack stands etc. Plus its nice to have enough room to move the car back and forth to find the correct location for proper torque weight. As mentioned, a 24 footer seems to hold their value well, as they are a popular size. If you have room for a longer trailer, I have seen some really good prices on used 28 to 40 foot long trailers, which often are listed for less than a 24, even though they were more expensive to buy new. But many people do not have the room to store such a long trailer, or it may require a more substantial tow vehicle to tow it.