As MightyMax says - depends where you live - here in the South East of England I would not have any worries about it. Neither the horses nor the rabbits have started growing their winter coat.
In general, what I have seen with our rabbits is that they tolerate cold (especially dry cold) much better than heat. Our Toffy was a garden rabbit and although she had a warm hutch, with the usual comforts - thick bedding - she never ever used it. Even in the winter she preferred sitting on the grass. On a similar note, the two I have right don't know what to do with themselves when it gets hot. They are totally flaked out, lying in the shade.
They don't like it when the weather is very wet but you can always cover their run.
