Continue to reward any approach to the crate. Then wait to click until he gets just a bit closer. Repeat a couple of times, then wait a little for a closer approach. Pretty soon he is right at the entrance, then you want a foot or two inside, finally the whole dog before you click. It takes a bit of experience to get it right, but you really can't screw it up much. If he shuts down on you, say "too bad" and walk away with your treats. Come back and try later. In my case, he kept working and we got the job done in one try. 
Ha, I know, forum posts are like a novel sometimes - except sometimes you don't always find out what happens at the end. There are lots of posts here where I'm like "well, what happened?!"
The long and short of it: we have a "success story".
He's always been kind of a strange dog, never doing things by the books. For his anxiety…...nothing I did really helped him.
I originally put him on Prozac as a last resort, but overtime he just improved on his own; I know it's not due to the medication, because he's been off of it for awhile.
He still hates confinement but he's learned that once he's in...he's not getting out. SO he basically goes through cycles where he'll whine for about a minute or two every so often (30 minutes to 2 hours) or so then goes back to sleep, until I get home. It gets better and better each time.
One of our biggest issues I think was him being able to escape, and that fear was feeding off itself. In the beginning he would pull out all the stunts to try and escape, some of them working of course. Once I made it so he could not escape, the major destruction and psychological issues died down. I ended up putting wood pieces around the crate (as suggested above) and that helped immensely to fortify the area.
He still does cry, and rip things up while I'm away...sure. But, as long as he isn't endangering himself, getting too worked up, or making a huge racket? It works.
After we got that solved. I moved onto trying to get him to be ok in a crate - which has been successful. He goes into it fine, lays down and doesn't cry a whole lot, or try to escape.
I think his 'anxiety' is not unusual, or inappropriate. Just a natural fear that dogs have of being alone, confined, and in a new space. I also didn't go over 30 minutes when I was teaching him as a puppy....big mistake.
Things that have helped: Music, not having the light on, making the pen one giant bed (instead of allowing an area where he could stand), leaving random tissues around in the pen, not letting him out of the pen directly after coming home, giving a single cookie before leaving and returning if quiet, having the area be inescapable obviously, and brushing his teeth if he comes out of the pen right away.
Things that didn't really help: thunder shirt (was working until he ripped it up), medication, mirror outside of the pen, leaving delicious food or toys inside the pen, DAP diffuser, etc.
