I had a horse that HATED to be trailered!!!! His 1st trailer ride was from Kansas to Tampa, Fl, so I can't say I really blame him. I tried several different ways & techniques, & it was always a crap shoot if he would load or not. Then we met a "Cowboy preacher" who used Horace for a Sunday Church demo. There are 2 differences....the horse that REFUSES to load, & the horse that CHOOSES not to load. Horace CHOSE not to load. After about 10 minutes of working with him @ church, he'll now load. I should say that we have a big rear load stock trailer with a step up.
Try to park the trailer parallel to a fence on 1 side. Leave the back & 1 side open for you to work him. Make sure there is a bucket with a little bit of feed up in the front. Doesn't have to be a full meal, a few handfuls will do. When leading the horse in, don't stand to the side or behind. Keep your energy up & walk up without stopping on a loose lead. Do not turn around. Keep your back to him & let him follow you up. If he hesitates, keep facing forward & have someone stand behind him to put pressure on his rear legs by standing back & spinning a rope. If he still is refusing or you are by yourself, then let the head lead be long enough that you can string thru the trailer & stand by the back doors. Pull in by the head lead while spinning a rope behind him. Remain calm at all times and don't rush him. Keep in mind, he's a big boy. You will not be able to pull him or push him in. He has to put himself in.
Once he realises that this big contraption will not eat him alive and there is a reward of a little feed up at the front, eventually it will get easier. Keep practicing & keep calm. At the church, I loaded & unloaded several times, the preacher loaded & unloaded several times, plus my non-horsey husband, & my 11 year old son. Brought him home, & a few days later loaded him up all by myself several more times with no more problems.
Don't quote me on it, but I suppose I'd say 2-Pak "chooses" not to load, based on how he will freely load when the trailer is just set out in the pasture. Any amount of pressure on him to load, though, and then he starts to refuse.
We've tried pulling him in before, like you mentioned, but it simply doesn't stick. More like, he'll brace against that pressure until someone gives up, the ropes snaps, or his halter snaps. One time or another that we tried it, he actually stood there bracing for nearly an hour, and then he started to move forward, so we let off the pressure a bit (using the whole 'pressure-release' system), and he violently jerked backward, reared, and then lost his footing and fell. After that, we tried again... only for him to repeat it. Four or five times in a row, though he didn't consitantly fall.
But it's like I said, I don't think he's actually afraid of the trailer at all. Once he's inside, he's perfectly fine. He'll stand there happy as pie, lead him out, and he'll just refuse to get in again.
My husband is not a very patient person either, & he's not into horses like I am. Brute force is his answer, too. Our kids show cows, & to get them in the trailer, then you tighten up the lead ropes & pull them up, having someone push from behind if needed. Ya can't do that with a horse. Horses are stronger on thier legs, and have more power behind them. And you know that horses pick up on "vibes", so by being tense & worked up, the horse will be tense, too. "Keep calm, baby" is my mantra for my husband when he helps! lol
I'm usually pretty patient with a horse, and when I do start to lose my cool, the horse goes back in the round pen and I just walk away. My dad, on the other hand, has no patience whatsoever... He won't give up and he won't listen to reason. He's actually gone so far as to run a lead through the trailer window and hitch it up to the winch on the tractor, and was about to forcibly drag 2-Pak into the trailer (But I unclipped 2-Pak's lead as soon as dad stepped away and walked him by his halter, back into the pasture.). As a result of that particular stunt, my father is no longer allowed to interact with the horses without strict supervision.