This is a really great question. The answer depends on the circumstances and the type of RV (Recreational Vehicle) we are talking about.
First let's take a look at what RV insurance is. RV insurance protects you, as a recreational vehicle owner, from excessive out-of-pocket costs in the event of a loss or if you are at fault in an accident that causes bodily injury or property damage. It can also provide compensation for your costs if you have a roadside breakdown.
RV insurance could be coverage for a camper, a travel trailer, tent trailer or a motor-home.
Just like every other type of insurance, you are required to purchase separate insurance for your RV in order to have maximum protection. RV insurance also has some coverages similar to that of auto insurance.
For towed RVs, the liability coverage on the towing vehicle might extend to the RV only while it is being towed. For example, you were going camping and attached your RV to your pick-up truck that is insured with company A. While driving, your RV accidentally damaged another person's vehicle. Company A, which is insuring your pick-up, might pay for damages to the other person's vehicle caused by your RV.
Keep in mind that the emphasis is on "while being towed" and might vary from company to company. Always make sure to check with your company to see if they extend liability to towed RVs.
Let's take a look at a scenario where your automobile insurance WILL NOT cover your RV. Say you parked your RV on the driveway and it accidentally rolled over to your neighbor's and damaged their garage door. In this case, your automobile insurance would not cover any expenses. It will be the insurance on the RV itself that will come into play.
It is very important to purchase RV Insurance separate from your automobile policy to cover liability, physical damage and your personal belongings.
Always discuss with a licensed insurance broker if you are unsure of what coverage you need for your RV.