A separate loading gate would make the most sense, but be aware that if your are running them into a normal trailer (one that doesn't lower to the ground) you will need to either build a ramp or block the area under the rear of the trailer or they will try to go underneath it.
If you use the 'rope them' method (I've done that), just feed the rope through one of the panel squares, pull them up against the panel, secure the rope and then reach through and grab a leg, you can tie their legs using pre-cut lengths of smaller cordage. Once you have all the pigs tied, you can safely enter the trap and remove them. Load them in the trailer (still tied).
I have piece of re-bar that I heated and bent one end into a 'hook', welded a 'T' handle onto the end. I reach into the trailer and pull a tied pig over to the side to untie it (always front legs first). But your trailer has to have panels large enough for you to reach through.
Spartans ask not...how many, but where!