I just got a quote for my horse trailer insurance, it was £107 with E&L, who lets be honest don't have the greatest rep' and only £55 from NFU, needless to say the decision was not difficult.
I am insured with NFU. When I insured my trailer, I added it to the car insurance, rather than insuring it separately, it was a bit cheaper. You might like to ask your car insurance provider if they will do that.