Contact the company that provides the coverage on the towing vehicle to get quotes for the travel trailer. Because of your existing policy, it will be easier for you to obtain additional coverage with a possible discount for multiple products.
Yes, it is one of many. A better place to look might be kayak.com, as Kayak looks at multiple sites like Priceline and finds the best deals for you. Other sites to look at would be Travelocity, Orbitz, and Expedia.