From what I understand,, An RV as in a Class A,B or C, an officer will only be concerned with what he see's in the driver compartment or within the drivers reach.
If an officer suspects something else further into the RV, any thing further than his reach will require a search warrant or your consent to search as this is considered the "Living area" and is considered your domain at the time being!
As far as a trailer,,,its a moot point, the driver cannot reach back there while driving so the officer should not be concerned!
I have worked the front gate at a few major sporting events, one did not allow alcohol to be transported into the event!
No One ever searched the vehicles and I can tell you,,, if you can't see it, there's nothing you can do about it!
Then you drive around the event later and find kegs going,coolers of beer and drink tables!
So bottom line,, be courteous and discreet and you will 99.9% of the time not have an issue!