This has me hopping mad! I've been a USAA member for a LOT of years (40+) and always had my TT insured through them. Now they're out of the RV segment and have partnered with Progressive for that. ...
The camper when off the truck is usually covered by homeowner's insurance. On the truck it should be covered by the auto insurance. I have had no problems with State Farm for insuring the camper with our homeowners and our auto insurance policies.
Not unusual for companies to offer low rates and then cover themselves by reducing the coverage or increasing the deductible or other aspect.