Kenny's approach is spot on...unless Jose Schmuckatelli drives his Toyota Corolla with his wife and three kids under your rear axles. Even if you are technically in the "right", a smart attorney might argue anything that gets his foot in the door, like how (insert your name here) shouldn't have even been driving this big truck because he isn't qualified to do so (translated: hasn't the proper DL). In short, you can be doing almost everything right, and still get kicked in the crotch.
Now, if you are minding your own business, like Kenny, and not doing anything commercial (i.e. not subject to the FMCSR'S) then, if apprehended with the wrong driver's license, you really only risk getting a ticket for wrong driver's license. Remember, only drivers & vehicles that fall under the FMCSR's are subject to out of service orders. (This is not to say that officer friendly may not threaten you with arrest is you persist in the same behavior.)
What many of you have failed to consider is the strong input from the trucking industry that drives many of these regulations to become legislation. True, safety is a concern, but the industry does not want you guys buying trucks and going into the trucking business & cutting into their market share!
Next. let's discuss what a "recreational vehicle" is.
TJ