I've got my Ifor Williams insured by NFU too! Can't remember how much it cost, as it's combined with the horses premium, but it was certainly competative, and they are a very good company to deal with.
Does that work Bridie? A friend of mine had that arrangement and when the trailer was stolen and she claimed they refused to pay on the basis that her trailer was not attached in some way to her house. Might be worth a check. It would be awful to find it out in the event of the worst happening.