Keeping rabbits outside during winter?

I have to male rabbits who live out side and this is there first winter will they be ok outside as it worries me , as ive said in my other questions they live in a big wendy house which is raised off the floor , inside the wendy house they have a hutch which is also raised so it doesn't take any room underneath up with a ramp leading to it and a cover over the wendy house for when it rains. It has a big bolted door so predators cant get it. Erm they have tons of hay and straw and ive bought them 2 snugglesafe heat pads is this good enough for the harsh weather we are bound to get?