I asked a state trooper (creeper cop) why they did NOT normally inspect recreational vehicles. I was told that federal law gives them the right to inspect commercial, but pulling in "citizens" without just cause is a no-no.
On the VERY rare occassion that Pennslvania pulls in recreational vehicles, it is a drive by (not a weigh-in) and they only INSPECT if they see an obvious safety violation (just cause). Kinda like a DUI check point, they can make you take the detoured route through thier inspection, but can only question you if they see a reason to.
SO drive right on by those COMMERCIAL CHECK POINTS unless there is a sign that says recreational vehicles/travel-trailers, boats, etc....