Is that a state limit on the class C and what is the weight limit?
We have a 26k lb or 15 passenger limit here in MO on a class C
It varies from state to state.
I know guys that own antique cars that have been pulled over and weighed for hauling with a 1 ton dually and a very large enclosed trailer.
Some guys have huge trailers since they own multiple cars and they wanted to have a single trailer to haul whatever they owned.
Cars from the teens tend to be very tall, around 7 feet tall, so they needed a tall trailer along with one that could haul a late 20's or 30's car that weighs in around 5,000lbs or more.
There are only a handful of antique car guys that have a CDL so they have to worry about any weight issues, mainly because most folks stay fairly local and don't haul long distances to attend events.
The furthest I have hauled to attend an event was from So Cal to middle of Oregon for a national meet.
But, that was using an open, flatbed trailer so overall weight wasn't an issue.