Insurance!

I believe Lance does lots of business in states where campers are titled, registered, and licensed as vehicles. They also must realize campers sold in the "cargo" states might end up elsewhere, and I suspect they provide lighted license plate hangers and certificates of origin for all campers. I believe what you are calling a serial number can equally be called a VIN.

I use State Farm for vehicles, home, and umbrella. No claims yet regarding a camper.