Apuff - seriously - there is no replacement for groundwork. Be it 10 minutes or 10 days, take the time it takes. Then, whenever you want to travel with your horse there is no stress, no trauma, no possible damage to him or yourself, and it will only take as long as the two steps up the ramp! Use blackmail if necessary - put a hay net in the trailer, leave it open, allow the horse to enter of their own free will to eat and leave again as they please. If your trailer has a ramp, have them walk ´across´ the ramp, not into the trailer, so they become accustomed to the sound and possible movement without the additional stress of going into a confined space. Make the trailer as open and light as possible. If you have an exit door, open it. Windows, same thing. Light, turn it on. If it is a step-up trailer, put some food just a reach away, so they need to step up with their fores. Don´t ask for them to reach the top of the mountain the first try, or 5th if necessary. Reward every positive move, ignore everything else.
As for protection. My experience is that, for long journeys leave your horse as naked as the day he was born. He will be (should be) traveling in a vehicle with air-suspension, air-conditioning and a hay net under his nose. He will have regular breaks to drink and un-load to stretch his legs. The shorter journeys require some protection. They are usually in a trailer or small lorry. But use proper travel boots, not constrictive polo wraps, and don´t, but don´t, wrap their tails. The photos show what happened to the tail of a friends horse, wrapped by a "professional" horse transport company. He arrived at his new destination with a necrotic tail which fell off when they removed the wrap. Even constantly wrapping too tight for numerous short journey´s will eventually cause a cut in circulation and the same results. If they are prone to "sitting" on the rear bar, you can get quarter guards, which are held on with a surcingle.