The police have to suspect that you are doing something illegal before they can legally stop you and ask any questions. That said, if you are in a wreck, it might be standard practice to get the weight of all vehicles involved, and note that on the accident report. Along with towed vehicle braking system information.
I know one California accident that resulted in a ticket. The owner of a F-250 was towing a really heavy fifth wheel, and it crashed. The insurance company wanted to 'step aside' - a legal term to not cover a accident involving a overloaded vehicle, or say drunk driving, or something that is excluded from your insurance policy. However the insurance did have to pay the claim, because they insured both truck and trailer.
The CHP found that the weight of the truck and trailer exceeded the Ford towing ability for that truck.
Have fun camping!
Fred.