I guess there's some logic to the ranger's position but I'd like to know if it has been challenged. A non-lawyer here but I know there's seldom a simple answer; however, the Code of Federal Regulations says this about resident camping under its list of prohibitions:
"(b) Construction, reconstructing, improving, maintaining, occupying or using a residence on National Forest System lands unless authorized by a special-use authorization or approved operating plan when such authorization is required." (36 CFR - Title 36—Parks, Forests, and Public Property)
I guess you could say the person was "occupying" a residence--his RV--but I'd argue the rest of the language implies a permanent structure. The USDA offers these definitions that I'd take to support that interpretation:
"Camping means the temporary use of National Forest System lands for the purpose of overnight occupancy without a permanently-fixed structure.
Camping equipment means the personal property used in or suitable for camping, and includes any vehicle used for transportation and all equipment in possession of a person camping. Food and beverage are not considered camping equipment." (http://www.fs.usda.gov/Internet/FSE_DOC ... 054750.pdf
As a full-time wanna-be, I have to admit some sympathy for rangers dealing with a flock of folks wandering from site to site in the forest. I expect it's localized as I've seen plenty of places with 5th wheels parked in out-of-the-way places and vehicles leaving for work in the morning, or so I presume.