Class A: After searching for over a month, the shortest Class A I was able to locate was 22'. Class A eliminated.
Class B: During the same search period, all of the Class Bs I found fit the length requirement (no surprise there) but they fell short (literally) in one dimension I hadn't considered. I am 6'1" in height and none of the Class As I looked at allowed me to stand straight up! Class B eliminated.
Class C: I feel just like Goldilocks! Class C is just right: available at 20' or less with plenty of headroom. Although there are few Class Cs around that fit my length requirement, I was able to locate a few for sale within 200 miles of my home in Southern California.
Now the only really important criteria remaining were amenities and condition. More on that tomorrow!