Copy and paste'd from rule book. My copy from 2008, might of been changes in the one or two newer additions, so double check. Appears to me rear window on motor homes are legal if they comply with below. (I know for sure the OEM's got water pressure spec's changed (lowered) in newer additions, so for sure double check). So a lot depends of date of manufacture to what rules they play by.
6.4.3.5
Vents or windows that can be opened for ventilation shall not be installed in the rear wall of motor home and truck campers. 6.4.3.6 Normally unopenable alternate exit windows shall be permitted in rear walls.
6.4.3.7 Rear entry doors with fixed windows shall be permitted in truck campers.
6.4.3.8 Rear entry doors with fixed windows shall be permitted in motor homes, provided that no combustion exhausts discharge from the rear of the vehicle.
2003 Majestic 23P... Northwest travel machine
2013 Arctic Fox 25W... Wife "doll house" for longer snowbird trips
2001 "The Mighty Dodge"... tow vehicle for "doll house"