I have always let mine play in the rain, but always dry them off once they are done. Ive the covers on the runs to keep rain out anyways, but they have all liked free ranging in the rain. Obviously if its really chucking down then I don't let them out :lol:
There was one tiny corner of Buu's hutch that wasn't covered so a little rain got in and she used to squash herself up in that corner and just sit there getting wet :roll: