Welcome to YT. Sorry Rocky is not being himself.
Is he eating alright? Is anything else going on?
I know mine are more lethargic during the winter -- they love to be outdoors and this weather doesn't allow it.
Sounds like his crate is a place of comfort - a lot of dogs like to just feel secure in their crate.
It was 58 here today in Iowa - hope this warm weather is coming your way and you can get outside, and see if that perks him up.
When was the last time Rocky saw the vet?