USAA, who uses Progressive for their carrier. Have had Progressive for 10 years and had no claims so I don't know how they'd do in a pinch. Since we've had no claims our deductible has been reduced to zero so that's kinda nice. We're currently paying $950/year for a 32' MH. I know your trailer would be much cheaper. We went through Hi-Sage rather than USAA since they were recommended by the first dealer. Everything else we have is insured through USAA and I'm sure you could go to Progressive indirectly through them.
2015 Greyhawk 29MV
Honda CRV toad with Blue Ox baseplate
Ready Brute Elite towbar with braking system
TST 507 Flowthru TPMS