Overhead Trailer Picket Line
Although the most common method is tying horses directly to the trailer, it has some faults, including the horse getting a foot tangled in the tires, lights, braces, etc. Portable corrals are becoming more common, and there are several other good ways to confine your horse and still keep him fairly comfortable and safe.
But one of the best tricks is the overhead picket line, stretched between two trailers. Depending on how far apart the trailers are positioned, quite a few horses can be secured in this way, and they have some freedom of movement - more than if they were tied to the trailer. Also, there's less chance of them getting tangled in the lead rope or somewhere in the trailer.
Hanging a hay net in front of the horses helps keep them occupied, and if they're inclined to fight with the horses next to them, a couple of squabbles will teach them to stay out of kicking range. Or a kicker can be tied on the far side of the trailer. Grain can be fed in nosebags, or by dumping the water bucket long enough for the horse to clean up his oats.
Look for more good tips in WH's Helpful Hints for Horsemen. The book is available online at www.westernhorseman.com.