Iv found snuggle pads pretty good, certainly better than nothing and much safer for outdoor use. I wouldnt run an electrical one outside just incase, the type i use have a connection down the wire so certainly wouldnt be safe.
Mr snugs kennels can be found reasonably priced, should be less drafty than a carrier. I think i got one on ebay.
Its horrible to see them out when your own are happily indoors all warm, theres 5 cat owning houses in my street and 3 of those shut theirs out with no cat flap or shelter
saggy belly is in his late teens and badly arthritic, he now uses a kennel in my garden as the petporte keeps him out of dexters converted pad, i often wonder why its me thats feeling bad when the owners dont give a second thought, they arent even nasty people just self absorbed in their own lives.