I had a trainer do this pretty much the same way and had my mare standing relaxed and comfortably locked in in 10 minutes when I couldn't do it in countless tries! She said my mare was "conning me" and just didn't want to be told what to do. I agree. She is a dominant mare and was very relaxed the whole time. I know I just need to be more confident with this.
The problem I always have is all the training books and advice tell you how to load but then pretty much say, "now close the door a few times and off you go". My mare will stand happily all day in the trailer as long as you don't try to lock her in. As soon as I touch the buttbar she charges out backwards.( I have a two horse straightload with a ramp. She's fine going up and backing out relaxed. ) My trainer just said "ah ah ah" and poked her on the rearend with the butt of a whip and then she stood still and she closed her in. I haven't tried since then for fear I will fail at this with no one there to help. I don't have this trainer around anymore. So, how do you close the door without them charging out when they feel something touch their rump? I've tried lungeline etc. to get her used to feel of something but she does the same thing. I've done tons of loading and unloading with her and its gone well until I try to put up the buttbar. The books need to address the locking in part because they just end at the loading part.
Any insight would be greatly appreciated.