When winter comes I sometimes sense an air of panic regarding rabbits who are kept outside. We relate their feelings to our own which to some extent is right but not entirely. Often a customer says - they are are sitting outside in the cold and I am worried about them!
We would suggest the rabbit that has plenty of choice will know what suits them. The connections link different zones and a small space is quicker to warm up with two bunnies inside it. So a draught free small space is first on our list. This includes the den snug, top box and the hay hutch.
In cold weather moving is essential. If the rabbits are given supervised free play when it's very cold that is helpful and also an interconnected system involving wriggling and making their way around is ideal.
The underground temperature will be steady and feel normal to them so consider sinking a hay hutch or creating a mound around it to increase that natural warmth. A buried piece of pipe is not only fun but also good for hiding and good for warmth in winter and coolness in summer! No wonder lots of animals find underground living comfortable.
Our bunnies here at runaround are living long and well in their old age and they enjoy a system which includes the 8 x 4 run with a hay filled tray, a top box, mesh tunnels, and a clear dig with a den snug added for winter. We change the hay a lot, add straw when it is really cold and move the run every two days. The bunnies run about free when we do this. It really doesn't feel like we trap them at all, but keep them safe and happy.
In your small draught free zones add plenty of hay and straw (straw is warmer) and refresh it frequently. The rabbits will burrow into this on colder days and snuggle together. They can provide their own form of central heating by staying close, breathing warmth into that small space and enjoying their full winter coats.