It sounds to me like you need to do a lot of ground work AWAY from the trailer. When you have him where he follows commands without kicking, rearing, or fighting you away from the trailer you can work on loading. During this time working on a "go forward" cue is also a good idea. Once he gets the idea (which will be similar to the initial sending away on a lunge line) you can send him forward through jump standards, over boards, whatever. This will help because you can use the cue when you get to the trailer.
Once you have ground manners and respect handled away from the trailer you can start teaching the horse to load. Patience is key. Remember, if you get in a fight with a horse you will loose. Don't go about this with the attitude that you will "make him get in"; you will loose and you'll never have a horse that willingly walks up to a trailer.
There are a few techniques you can try depending on the horse. One I like is to make the trailer "rest" and outside "work" (this assumes the horse is not scared of the trailer itself, something you should work on before ever asking the horse to load). Ask the horse to load, do NOT expect him to just hop in the first try. Instead ask him to stand calmly with his head in the trailer the first few times. If he stands there calmly for a few seconds reward him with praise and allow him to leave (turn and walk away slowly at your command). If he refuses, jerks away from you, etc work him for a minute or so on a lunge right then (as soon as he pulls away from the trailer send him away and lunge). Don't run him into the ground or beat him around the circle; you need only keep him in a nice brisk trot for this to be effective. After a minute or so of lunging calmly ask again. Repeat. As he gets comfortable ask him to go in more, stand with one front foot, then both front feet, then all the way in, etc. The goal is to ask him to stand long enough to extend the time he is comfortable standing in the trailer, but also ask him to leave before he decides to on his own (always make it your idea for him to leave the trailer).
Don't expect him to get in in one day. He might, but it depends on the horse. Keep your sessions short. You don't want either one of you getting exhausted or frustrated. Always end on a positive note, even if a positive note means taking two steps back and having him do something from a week ago solidly and confidently. Patience and consistency are key. Work him often (every other day, or 3days on one day off, etc) for short periods of time and be happy with small progress if small progress is what you get. Don't get in a rush and push for a huge improvement unless the horse is ready to give it to you or you'll just go backwards.
You may want to consider having a trusted trainer work with you if you aren't experienced with working on ground problems and respect issues.