A good number of quotes to compare is three. If you already know three companies whose RV insurance you are interested in, go through each of their quoting applications. Then, compare the final estimated premiums and the features of its policy: maybe company A’s policy is cheaper overall, but company B’s offers greater coverage for a slightly more expensive price.
The underinsured motorist coverage works similarly, but it would only pay out when you get hit by someone who does have auto insurance, but your bodily injury damages that they caused are more than they carry, leaving them underinsured. Just like your bodily injury, the UMPD would pay to fix the damage to your car caused by the other driver, and you only have to pay the $250 deductible.