Unfortunately most folks ignore trailer/vehcile ratings and the police don't seem to really enforce it beyond commercial vehciles.
the thing is the combination "ratings" are merely suggestions. They aren't enforceable by anyone for any reason.
DPS enforces registration ratings. Unfortunately some states will let you register anything at any weight regardless of the engineered GVWR.
The federal (and most states) definition of GCVWR is the sum of the GVWR of each vehicle in the combination. For example, a pickup with 8,800# GVWR pulling a trailer of 12,000 GVWR has a GCVWR of 20,800#. If the trailer is homemade or for some reason has no rating stamped on the plate, the GVWR of the trailer is simply the weight as it sits.
Travel trailers 5th wheels happen to be exempt from the 26,001# line defining a CMV regardless of use.
when looking at actual, legally binding ratings, the axle ratings (steering, drive(s), trailer(s)) and the GVWR(s) are the only ones that matter. There is no legal definition of what something can or cannot pull.
physics defines limits though. Too little tongue weight and you've collided with something (which is
illegal) and too much and you will bust your GVWR or RAWR (or your tires).
The last thing that must be considered is the minimum speed limit on the roads you plan to drive. While there might be nothing illegal about your combination, if you can't keep above the minimum, you are subject to be cited for impeding traffic.