Generally when you are horse camping, you have the opportunity to tap into the experience and wisdom of other available campers who may share their own tips for overnight keeping, or even be willing to double check your set up until you feel confident on your own. This is one of the great things about horse people, we love to share knowledge and learn.
Of all the overnight camping methods for horses, high lining between two trees is likely the most safe and convenient method. With this method, all your overnight equipment for your horse can be easily packed into a single bag lightweight bag. You can even pack your high line equipment and carry it with you on the trail, trekking off into the wilderness to camp anywhere your heart desires, and the law allows. Now that's freedom!
Instead of wrapping the rope around the trees, use Tree Saver Straps to prevent the trees from being girdled and dying. This is a good piece of equipment to become familiar with as many wilderness areas require them.
If tying to a tree and your trailer, be sure your truck is hooked on to stablilze the trailer. Many who do tie between a trailer and a tree report that sleeping is disturbed if camping in living quarters (better to consider that before losing that night's sleep!).
The following is a fantastic instructional video from Trailmeister.com
It is rarely ever a good idea to tie your horse to the trailer overnight. There are simply too many opportunities for injury, including slipping under the trailer (yes, it really happens). When no other option is available, it is better to house your horse over night inside the trailer, rather than tie to the outside of the trailer overnight.