I use a completely different method. Using a carrot stick or other solid stick I ask the horse to walk in the trailer if he hesitates start bumping stick on his back/bum one step is enough for me to stop.
If he runs back keep his head facing into the trailer steady pressure but not pulling and keep bopping with the stick. Harder each time. If he continues to run back start circling him fast then allow him to stop at the trailer and return to asking him up. Pay a step at a time. Then ensure you can have him stand there still with the gate down. A tap on e bum with the stick if he starts to shift back. Make sure you're not rewarding his backing up by dropping the pressure. Keep yourself to the side/ in front.
Once you've got it mastered at home practice in different environments, a neighbours property or local park.
Also be aware of your driving when floating
I use this method. So many horses are 'accidentally' trained to back into pressure from behind when float training. They go backwards into the pressure, handler panics and takes the pressure off - 1 point horse, 0 points handler. Horse has just learned that running back means removal of pressure.
I never allow the horse to turn away from the trailer. He can run back for km's if he wants, but I'll keep tapping away at his backside until he stops and takes a single step forward. Then the tapping stops immediately and he is comfortable again. Ask gently for him to walk forward with a light touch on his halter, if he doesn't move forward, threaten to tap him, and if he still doesn't move, start tapping again until he steps forward.
A pet peeve of mine is people using food rewards to bribe a horse into the trailer.
This is getting the horse to focus on the food, not on the trailer or the handler. It tends to end up with the horse running in, grabbing a mouthful, and running out again. Also dangerous and near impossible to do on a particularly difficult horse, with one person present. And then folks, what happens when you go to a show, over 2 hours from home, and you find you don't have any food bribes left at the end of the day, or the horse feels like it's not terribly hungry and wants to stay with his new show buddies?
I have to have a bit of a chuckle at the end of a show day, you are guaranteed to find some silly soul trying to convince 'old Neddy' to please come onto the trailer, shaking a little dish of pellets, pulling on the halter and standing in the middle of the bay of the trailer, while Old Neddy is happily leaning back in his halter, neighing to all his new friends. These people tend to be the ones left at the grounds after everyone has gone home, 3 hours after the competition finished, dark gathering, in tears begging the horse to come onto the trailer, with promises of 5kg bags of carrots, all the massages and grain that he wants if he'll just come home!
I NEVER enter the float with the horse, until the back is secured. One of our Para-Olympian's lost her mother in a horse trailering accident - she was in the trailer with the horse when it went ballistic and she got crushed to death.
1) If you pull, the horse will pull back
2) We teach horses basic respect lessons - to NOT step into our space. So standing in front of the horse, on the ramp, pulling on it's head trying to drag it in will simply result in a horse leaning back into the pressure and thinking you are a crazy bafoon.
3) Please, for the love of god, do NOT tie the horse into the trailer before doing the back up. This is how horses panic and break their necks, backs, and legs. Very, very, very bad idea.
Safest way - driving a horse forward. If the horse respects that it will get tapped on the backside if it goes backwards, it will work out quick smart that its a heck of a lot more comfortable inside that trailer than outside. Then you have no need to go inside the trailer, the horse walks up the ramp on its own, and all you need to do is shut the breech gates behind it, lift up the ramp, and go around to tie their heads. Minimal risk ;)