What is the proper/preferred temp with a heat lamp to keep rabbit hutch...

[Renee]

...outdoors in the winter? This is my first rabbit, I believe (we found her) she is a Rex or a Havana, looks similar to both it's kind of hard to tell. Not sure how old she is but I know she's not a baby, gave her various snacks and it didn't mess with her digestion (like it's warned it will if they are babies) so that's why I don't think she's that young. My husband built her a hutch with a small nest area and run. We will cover it and insulate/shelter as much as possible, it's unfortunately not an option to keep her indoors as we live in an extremely small house right now. We have a lamp but I cannot find anywhere online where it says how warm it needs to be. I know they cannot deal with high temps but I don't want her to freeze, where I live it gets VERY cold. Also, I've heard there are a few medicinal precautionaries I can take before moving her to the outside house? Please, any advice would be dearly appreciated! Thank you