We bought our first motorhome
SEEN HERE in the fall of 1983. It was right at the time the 1984 chassis became available. The Mirage motorhome model year was a 1984, but it was built on a 1983 Toyota chassis. The vehicle title stated 1983 (matching the year of the chassis). Our insurance company at the time (Allstate) considered the year of the vehicle based on the 1983 title.
We owned that rig for 24 years, replacing it with our 2007 PC-2350. We ordered our PC in early May of 2007 and picked it up from the factory in late June. The mismatch of our first rig always bothered me, hence I made sure our 2007 Phoenix Cruiser 2350 was built on a 2007 Ford E350 chassis.
The only difference I know of between a 2006 and 2007 E350 chassis, was the color of the cab's interior, the 2006 being a dark gray, our 2007 being a shade of tan. There are no technical/mechanical differences.