I agree with Sal. Some 8' 2x8's work wonders. I use 4 of them. Position them so they stick out past the ramp a few feet so that the front tires are on the boards by the time the nose reaches the ramp. The clearance issues come at the nose and also getting high-centered once you transition onto the trailer. The boards give you an instant 1.5" of extra ground clearance where you need it and if the car is wanting to high-center on the boards, cut or arrange the boards so that they don't go all the way to the "peak" of the transition.

Not sure if you're getting an enclosed trailer or open trailer? If you get an enclosed trailer, do yourself a huge favor an get one with a 4' escape door on the driver's side so that you can open the car door all the way with the car on the trailer. No matter what, if you get enclosed with an escape door or an open trailer, you'll probably have issues with the height of the car and clearance to the bottom of the door to the trailer fenders. I solved this issue by screwing 2 pieces of 4" thick bridge plank to the floor of the trailer for the car to sit on....raises the whole car up 4" on the trailer so the doors have clearance to open over the fenders.