Unless it's a convertible, I also highly recommend an escape door. I custom ordered my trailer just so the door could be exactly where I wanted it. I had the fuel pump fail pulling my Daytona out of the trailer after the car had rolled back about 2 feet. Took me almost 30 minutes to wiggle my fat *ss out of the car inside the trailer...
Something else to consider.... A Mustang is generally 3000 - 3600 pounds. The trailer is around 3000 pounds. With 2 3500K axles, that doesn't leave a lot of room for tools, etc that all tend to weigh quite a bunch. Personally, I'd look for a 20 footer, escape door, 5K axles.
If you are ever going to have to borrow it in a pinch for a Lightning, go for a 24 and always have a real skinny friend around to help get it out of the trailer. Just ask Vinny T
