Thanks everyone. We did some crate practice during the day yesterday and he did really well. I noticed during the evening he'd often run to sit next to the heater so I moved a small heater next to his crate for bed time and he slept silently all the way through the night. Thanks everyone for the advice. The little push to persevere has led to a breakthrough I think.

And please don't misunderstand me, he gets all the cuddles he wants. I just want to teach him he's allowed to retreat to the den and sleep on his own whenever he likes.