Incidents that aren't auto-related.

Your auto policy probably won't protect your rental against non-auto accidents. If, for example, a cooking fire inside the motorhome damages the vehicle or injures someone, your auto policy probably wouldn't cover the incident.

Motorhomes with more than four wheels.

If you rent a motorhome with more than four wheels, your auto insurance likely will not cover the vehicle. In this case, you might want to purchase a supplemental motorhome rental insurance policy from the rental company.

Other drivers.

Who's driving the motorhome might matter. Depending on your insurance company and the state in which you're insured, your auto policy might extend to a rented motorhome only if you (the insured person named on your policy) or your spouse is driving. In other states, the auto insurance policy would apply to the motorhome even if another relative who lived with you (your adult son or your live-in father) were driving.