I think I learned something with my last two panthers that I wish I'd known for all of them. The way I figure it now, being locked in a cage and then having a big hand come reaching in towards you, where you're cornered, and then have the hand chase after you trying to grab you or scoop you up is just plain starting everything on a super traumatic foot. It's like starting the relationship off in a way that terrifies the poor guy/gal.
So what I did was leave their cage open and put a fake tree or plant in front of their cage so that they could come out on their own. The first couple times I let them come in and out as they wished, which usually took hours of me sitting on the floor of the same room (to be lower and less scary) watching tv on my laptop. Then once they seemed comfortable enough to come out of their little "territory" I tried putting my hand in front of them to use as a bridge between branches or to climb on. Then I'd hold them for a couple seconds (seriously, only a couple seconds) and then put them back. Short enough so it's like "omg I'm on a hand! Oh, now I'm off again and I'm ok... cool." Then I started increasing this. After a couple weeks they were getting shoulder rides to outside time in the sun or stuff like that.
This, along with hand feeding, seemed to make my last two panthers very much tolerant of handling. They don't by any means love it, but at least it's not a fight to get them to the vet or out for a cage cleaning. I wish I would have tried it with all four and seen if it worked well on more chameleons. But it may be something you can try.