Hey there,
Just to add to the comprehensive list of the previous poster. If travelling with only 1 horse make sure horse is travelled on the right hand side of the trailer. This is to keep trailer balanced against the camber of the road. It was somnething alot of people are unaware of.

oooo also check with your breakdown insurance as to if you are covered for breakdown with a loaded trailer, i have heard that sometimes this can be contentious and in fact that reminds me I need to check my policy with RAC...good memory jog!! lol