Winter Months

I'm a bit worried; It is getting quite cold here now, and although I bring my Bun in until around 10:30 PM I have to put him back out again, as my landlord wont let him stay in doors. So I have smothered him with alot of hay, got blue waterproof sheeting ( two lots), but what else can I do?

He has a snuggly tunnel which connects to his hidey hole in his hutch, and I put a blanket under the sheeting to keep warmth in, and an old fluffy body warmer in his hutch ( He hasn't shown interest in chewing fluffy things.).
He has a winter coat, because he is generally outside, is there anything else?

Rabbits can cope with cold very well, -20° Celsius are no problem when they have a good hutch that protects them from draft and weather and when they have the chance to adjust.

What is a bigger problem are changing temperatures, that's hardcore for their respiratory system, better leave them out in the cold all winter than bringing them inside for a few hours. Imho that also could compromise their winter fur.

Your setup sounds good, I would just be wary to bring him into a heated room.

Oh. I hate leaving him out there. But aye, you have a point, I just have contradicting information on the internet. It says if I was to bring him in for a few weeks and put him out, then he'd lose his winter coat. So i'm stuck what to do for the best.