You'd be surprised at how resilient they can be
I'd personally just start offering snugglesafes if you are concerned, if possible, mount them UNDER the hutch (if they live in a hutch/run setup which i think they do?) so the warmth just radiates up and through? Top up the amount of hay etc, but as Ali says, do your best to not go crazy so they develop a naturalness.
It really isn't that cold right now, yes, its going down to 6-10 at night, but its not crazy cold yet, they still have a fair amount of time yet to sort out their coats.
Biscuit is going through a stupid moult atm getting ready for winter, you may think that sounds odd for a housebunny, but due to Ginger, my office is always similar temperatures to outside as the window is ALWAYS open, so they do feel the difference between the air, they just dont have hthe wind to deal with.
His undercoat is AMAZINGLY thick, and i mean :shock: thick! The stuff coming off him atm is so soft and thin.
Ginger still hasn't even finished her first ever moult :roll: :lol: