mkirsch, the world may not work this way, but the California Vehicle Code sure does.
Positioning of Plates
5201. (a) License plates shall at all times be securely fastened to the vehicle for which they are issued
And as far as trying to put words in my mouth, I've never, EVER laid claim that I'm suddenly an RV. The CHP is gonna look at my registration if he stops me and see that the truck I'm driving with a camper in the bed is not an RV but instead is a commercial truck. (Pick up trucks in CA are commercial if you want to put anything in the bed at all if over 8,000 lbs. Pickups with an unladen weight of 8,000 lbs. don't pay the commercial weight fees.)
I've plenty of CHP acquaintances and they have told me that they can and will site someone who has their plate mounted to anything other than the vehicle for which they are issued including a camper if the driver tried to educate them that they are right and the officer is wrong.
I learned that when I was 16; the ticket will have the VC violation on it and all my arguments won't matter. All that matters is the language in the law.
So, enjoy what ever laws NY has and I'll enjoy what ever laws CA has.