I just measured our 29b and it is 9'6" from the ground to the extrusion at the top of the side. Then there is the sharp curve where the roof meets the sidewall. + 3 1/2", then the fridge vent on the sloped roof + 4". So just in from the side I'm over 10'.
Don't forget the ladder going up and over, mine is on the back but realtivley close to the side, max air covers.
I would go with a 12' wall, maybe 11' IF the framework went to a minimum clearance of 12'+. That would be the minimum if you are backing under from a level driveway.
Ken