Were you going to get some panels and put a round pen up? If so, just put them in that until daylight. It would be safer to make a nonstop trip if possible, instead of tying to the trailer in a strange place. I've had horses break halters, lead ropes and the welded trailer ties when they felt like it. If you do stop to wait awhile, just leave them in the trailer - give them some food and water.
I don't think I can afford the panels by then. We are having to get the water on, build a shed, wire etc. I don't plan on taking them out until we get there but after we are there I was going to tie them to the trailer til daylight. We have the option of leaving Thur evening or Friday morning. We are leaning Thur. We may have to stop and rest awhile though.