Keep his nose pointed into the trailer. I'd take out the divider to start with more room for both of you.
I'm not sure of CAs methods but probably can't be that much different to Parellis right?
I take a dressage whip or carrot stick or lunge whip, preferably carrot stick with string off as I've had it catch in the hinge before.
Walk him up like nothings wrong ask him to step on to the ramp by driving him with hand or stick. I tend to place myself slightly in front, preferably in the trailer out of jumping around range.
Take a feel on the lead and tap again very gently at first on back, sides or bum remembering to increase the pressure to as much is needed. If he runs back keep his head towards the trailer and dot let him stop, Keep him facing the trailer and drive forward again, remembering to reward for each correct movement.
Get his hoof back on the ramp and let him relax.
Ask again tap gently and get as hard as you need. Repeat the process until he's in. It always helps to have a hay net in there too!
Once he's in the trailer give him a really good rest. Then taking your stick walk slowly out. If he goes to move out a tap on the bum should keep him there. Stay in his eye range for now, if he backs out without being told get him back in.
When he's shown he can stand there, doesn't have to be long just enough so he knows not to rush out ask him to come quietly off. Take a break, mostly for you as this can get frustrating. Then do it all again. Slowly increase the time he stands then close the rear doors, let him stand and open them again.
I spent 3 hours on this with my mare who was a HORROR to load.
She now self loads.
When it comes time to actually float it is IMPERATIVE that the driver knows how to float! Keep it slow and steady especially around corners. Bad floating is the main reason most horses become hard to load.