I thought the same thing when I purchased my Keystone Bullet several months ago and shopped my current auto provider, Geico. An entire discussion on Keystone's message board regarding pricing in certain market. Post #9 clears it up!
RV Insurance for my new Keystone BulletRemember, when towing, the liability portion of the insurance is covered by your truck's insurance. Comprehensive and collision is what you pay additional for with RV insurance. That's why is should be substantially cheaper than your TV.
By the way, by the recommendation of other experienced RV'ers, I ultimately decided to insure the TT with a different insurance agency (Good Sam) and got a pretty fair premium of $280 per year.