Regarding the size, if you're worried about cramming it in a car, I wouldn't go any bigger than the 42. I used to have a T-Bird when I still had 2 dogs and could fit the pens in my trunk just fine. However the tops are 48" and those would not have fit. I had to pin tarps across the top until I got a van. You could certainly get by with a 36 if you're worried about portability, as long as you don't have escape artists. With a 36 they can get their feet on the top row while still standing on the ground. But I know of a lot of folks that use a 36 for Basenjis. Also keep in mind the taller they are, the HEAVIER they get to lug around! lol
I've already started to realize that I need a bigger car if I'm going to start driving dogs around the Midwest. Guess I'll have to get a station wagon or an SUV. I'm not to the "van" stage yet. lol. I think I'll go with the 42", Nemo is pretty crafty at escaping from kennels and I'm sure the puppy will be up to no good when she grows up.