I have used a 20' enclosed for over 15 years. Great size for a 944. Can do everything except live in it with the car in it.
One friend has a 16'. Car fits, tire rack over the front of the car. Tools in the Truck. I think it is a little too small, but is can work. The 22' that Ron mentions is a hard size to find, but very nice.
Hope this helps.
Chuck
Chuck Sharp
San Diego, CA
1986 Spec 944 #58
Red / Twin White Stripes