Rolling, or ready to roll, it is treated as a motor vehicle. Parked, hooked up to services such as electric, water, sewage as in a RV park it is a residence. In assessing whether it is a motor vehicle or a residence for Fourth Amendment purposes, the courts will look at the totality of the circumstances to make a determination.
In United States v. Levesque, a 1985 case, the court disallowed a warrantless search of a motor home that was not readily mobile:
"The trailer at issue.... was situated in a trailer park and on a lot, objectively indicating that it was being used as a residence. Although the truck which tows the trailer was only a few feet from the trailer, the trailer was not readily mobile in light of the fact that one end of the trailer was elevated on blocks and that the trailer was connected to utilities at the campground, and also because of the three quarters of an hour lead time to connect the trailer and truck. The mobile home exception to the warrant requirement would appear to have no application herein."