It sounds like you have been going about it the right way. For whatever reason, he's just not improving.
A few things I have tried over the years.
Putting a shirt in the crate, that I wore that day.
Playing classical music on low.
Favorite treat, that they only get in the crate. Try for one that lasts a long time.
Moving the crate to different places.
Having it covered, or uncovered.
Taking my own pillow, and laying next to the crate. Yes, I was really tired when I did that.
Big stuffed animal in the crate with them.
Thicker dog bed.
Over stuffing the crate with (not hay) straw. It's messy, so don't have the crate on carpet.
Not all those who wander are lost.
Life is just a leap of faith.
Spread your arms and hold your breath and always trust your cape.
Two things define you. Your patience when you have nothing, and your attitude when you have everything.