I tow at the speed limit (mostly), get passed by hundreds of cars and semi's every trip (trailer speed limit in california). In 40 years of towing , no cop has ever had a reason to look at my trailer tires.
We have yearly state inspections in Pa. I don’t know if this particular state policeman would have done anything but I was stopped at a DUI checkpoint in Pa one night. We were backed up some and he already checked me out so he quickly looked over my car trailer. He said he wasn’t doing that type of check tonight but everything looked good and asked if he could show his partner, I’m thinking a new guy. He showed him my crossed chains and breakaway switch then they checked out my tires. He thanked me and said everything looked great.