I tried the slow enticing with food and after 2 hours totally lost patience and gave up on that tactic. Pete was not afraid of the trailer, he just didn't want to go anywhere and was being stubborn. What worked great for us was to have one person holding the lead rope in the trailer and a second person with a butt rope attached to the side of the trailer and then walked behind him. The person upfront was just to make sure he went forward. Don't pull or they react and back up. You can't win that way. Once the butt rope even touched his back legs he went right on. We use it with him everytime, but most times now he just sees it and walks on. If your horse is really sensitive or panics with the rope I wouldn't use it, but this method worked well for me.
Also, some horses have a problem outside or when the trailer is dark and it is sunny out. The change in light is hard for them sometimes. If there is room inside the barn or in an indoor arena try loading in there and see if it makes a difference. Good luck!