J.P.
What about the garage? For the cats, you can try putting some netting over them? I haven't had much success with keeping cats away from plants. Oh, maybe put them high, on a bookcase?
For the cold, if they are house plants, you need to worry about the dirt getting too cold for them, they aren't as hardy as outdoor plants. I think the sheet depends on how deep your porch is. on my back porch, I wouldn't worry, but on the front, I would have done the sheet too.