[Cool Hand Lurker]

The 15x8 should be fine. Most Model A's are about 14' long. The biggest problem I have had with car trailers is with the ramps and the angle they take down from the back of the trailer. Some of the lower cars will bottom out coming off the trailer. Even a 2' dovetail with a 4" drop will give the ramp angle a much more gentle slope. With a 15' trailer you have room to put a dovetail on. Another alternative is a modified ramp shaped like a dovetail but either way you can cut the angle coming off the trailer in half.