I think it is very important to keep some of these things separate in your mind.
The federal guidelines on CDLs and CMVs only take effect when you cross a state line for commerce with the exception of a limitd number of hazmat items that are always regulated. If you are never leaving your state, forget about them.
Each state is free to define a CMV and the requirement for a CDL for purposes of intrastate use. They have to enforce and comply with federal regulations too but only for commerce. If you are not in interstate commerce the federal regulations do not affect you but the state ones might. In some states the rules are srticter than the federal ones, in other states they are less restrictive.
For instance, in New York the DMV regulation which categorizes who needs a CDL and what class it needs to be reads "A CDL is required to operate a COMMERCIAL motor vehicle that:" and then it list all the vehicle types. So, for NY no commercial use = no CDL.
Again, in NY, the regulation for air brakes begins: "An air brake endorsement is required to operate any CMV that is equipped with air brakes or air over hydraulic brakes." No commercial use = no air brake endorsement.
Other states may use weight (laden or unladen) or the number of axles or just about anything else to define the requirements.
As for tossing camping gear in the bed of a cargo truck and calling it an RV from the way the rules were explained to me that won't work. At the time I was looking into buying either a road tractor or a medium duty straight truck with a sleeper and shortening the frame to us it to haul a large fifth wheel camper. In order to be able to register it as an RV and not as a commercial truck I wanted to equip it as an RV.
An earlier post here listed the stuff an RV has to have. The truck dealer (who had done several truck to RV conversions) showed me one conversion done in a large tractor sleeper. And no, you didn't need a CDL or air brake endorsement.
They had a microwave oven, the bed, one of the portable toilets that you remove the tank from to empty, a 5gallon water jug on a shelf with a spigot in it etc. A camp stove would have worked too.
The key point he brought up was that it needed to be in a space not used for general cargo. Now, with the advent of toy haulers I'd guess this line is getting blurred too since the rules seem to envision a permanently enclosed space. I don't think that a fabric covered truck bed with a few bits of camping gear in it is going to fool anyone into calling it an RV. A commo shelter with turnbuckle tie downs might.
I have learned that when asking commercial vehicle enforcement folks about rules related to MVs and RVs to ask them to specifically state what section of vehicle and traffic law they are citing. Without exception those rules have been predicated on COMMERCE. Note that this has been in New York so don't think I'm writing gospel here. So don't just ask a cop for an answer, ask for an answer with a specific citation of code....
An earlier post stated that if you do not register a deuce or 5 ton truck as historic then NY will register it "Commercial". That is correct even if you are not involved in commerce since NY classifies all vehicles over a certain weight under commercial registrations even if they are never used in commerce. 3/4 and 1 ton trucks get commercial plates even if the don't spend a day in commerce over their entire life span.
Don't confuse that plating requirement with a CMV or CDL requirement. Like most states (or the federal rules) unless NY does a top to bottom re-write of it's vehicle and traffic law all at once to reflect modern vehicles and uses there are going to be flaky situations like this. Back when the rules were drafted soccer moms weren't driving F-350 crew cabs or towing 8 horse trailers and 14,000 pound campers. Thoase of us old enough to remember the '60s and '70 will tell you that seeing a pickup truck in a residential neighborhood was unheard of except for contractors.
So, after 6 pages of comments all we really know is that you need to know the rules in every state in which you are going to operate your MV and that you may need to keep the requirements for a CDL separate from those for a CMV, from a commercial plate, from scaling requirements, from mandatory stops at commercial vehicle enforcement inspections etc.
Lance