It was called a Winnebago in the movie, but it was really a modified GMC. Funny enough, the GMC motorhomes fetch a pretty penny these days. They were front-wheel drive with usually an Oldsmobile 455 with transaxle. In the end of its production, they were powered by the 403. The rear suspension did not encroach into the living space with a hump, and they were close to the ground for easy ingress/egress.
Check this link for more information on them: http://gmcmotorhome.com/
Thank you for the link. Will read later.