I keep seeing so many stories about fiberglass walls delaminating and the such with luan as part of the construction. I see people who don't even have water damage and the walls are coming apart. So...
When we were shopping for our latest RV (sixth), my requirements were either Azdel or stick & tin construction. We wound up with stick and tin.
I know if we ever get a leak, it's a matter of removing the siding and repairing the damage with regular carpentry tools. You can't do that with a laminated wall.
With Azdel, I would have been willing to take more of a chance because the wicking effect that luan has would be eliminated.