Sorry we couldn't respond until now. Everything in the following paragraphs is Cyndi's explanation. She wants to emphasize a couple of things... this is legal information, NOT legal advice. Also, this is general information, not necessarily applicable to all states or federal jurisdictions.
1. A search warrant is needed before searching a "residence." There are exceptions to this including, but not limited to, exigency, consent, checking the welfare of someone inside or a parole/probation waiver of 4th amendment rights.
2. Motorhomes, trailers, campers and popups may be considered "residences" requiring a search warrant, by the courts.
3. Factors determining if something is a residence include, but are not limited to - is someone actually "living" there? For example, are there plates, silverware, bedding, food, a fridge, stove, clothing, personal items - indications that the individual is using the RV for the activities associated with the privacy of the home? And, in the case of RVs, is there a clear indication that it is not simply being parked/stored? Does the individual occupying the RV have "standing" (can they claim 4th amendment rights there?) For example, do they own it, did they rent it, do they have the owner's permission?
4. To complicate matters, many jurisdictions consider motorhomes and campers to be "vehicles," and popups and trailers to be "residences," (for purposes of "residential burglary" - a more serious crime than "vehicular burglary.") Also, the Vehicle Codes in most jurisdictions consider motorhomes and campers to be "vehicles" when out on the road, whereas trailers, etc. are not, as they are not being "driven." With traffic stops, the courts may also consider the potential for loss of evidence, due to the "mobility" of RVs on the road. These distinctions might also be used by the courts in determining whether a particular type of RV is a "residence" or "vehicle," or whether a search warrant is needed, during a traffic stop.
5. Additionally, some "regulatory" law enforcement/agencies, such as Fish and Game, Border Patrol, Agricultural Inspectors, etc. often have the legal authority to stop and search without a search warrant.
6. Often, there are no "black and white" answers in the law. Different jurisdictions and/or judges, will frequently rule differently on the same issues, and the legality of any search will be determined by the courts.
7. Finally, in most jurisdictions, it is unlawful to resist even an unlawful search or arrest.
(This is Kev again) I hope this helps the OP and others. I knew, when I saw the questions, that there weren't going to be any black and white answers, and while that's unfortunate, it is what it is. Cyndi spent a lot of time trying to word her answers, so they'd be as clear as possible, but we're talking about the law, and as everyone knows, there's a LOT of ambiguity.
Kev