US Rider is great -- I HIGHLY recommend them and have used them several times. I wrote a review here:
http://www.teamflyingsolo.com/2011/03/why-i-keep-forking-out-130-every-year.html
And sorry, fh, but AAA will not touch your horse trailer with a 10-foot pole, not even under the RV plan. Before I had USRider, I had AAA and when my truck broke down on one cold November night on the side of the interstate, they happily offered to tow my truck--leaving trailer and horse there in the dark. Even if I got another trailer to pick up horse, they would still NOT tow the trailer. Of course, I didn't give a darn if they set fire to the stupid truck -- what I cared about was standing in the horse trailer! It was horrible and there are many others who have had similar experiences. I got home, immediately canceled my policy, and called USRider.
When they pick up the phone, their first words are "Are you and your horses safe?" THAT is what I want the priority to be!

Solaris -- 16 hh Appendix Quarter Horse = MY DREAM COME TRUE!
We Are Flying Solo