I have found over the years that it is just easier and just the right amount of line to buy the trailer ties and just use them instead of your lead rope. This way incase they break the trailer strap you still have your lead rope as a back up or for when you get to where you are going. Depending on the horse I either then take off their lead once they are clipped to the tie strap or I will loosely tie the lead around the neck. But even using the straps some horses will just rock a trailer more than others. Hope this helps.

I always carry a coupe extra tie straps and leads in the trailer just in case.