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Big ole round gas fired wooden tub.
Somewhere on this forum is a picture of a 'Rednek' Hot tub ( not a spa).......... THAT, is what your Hypothetical friend is looking for!!
First, I agree that a used HotSpring might be a great way to go. I am going to do that for my own cabin once we get the thing built. May even do it before we get the place built to encourage the contractor a bit. I know a guy who sells wooden hot tubs - actually, two. One is me, and the other is Andy from Robert's Hot Tubs. I would say that they are more set up to do shipping and the like, so you may want to check them out. They have all sorts of equipment kits and so forth. I have met both Andy and Robert, and they are good people. Ask them about the cold envrionment - most large wooden tubs do well in situations where the tub is outside and the plumbing and equipment is inside. Could be under the cabin, in the garage, or what-have-you. But the huge volume that most of the bigger tubs hold gives them great staying power before freezing. Most are set up with freeze-protection which can turn on pumps or heat in your absence if needed. Since your bud doesn't seem to want a fancy schmancy setup, two pipes between the tub and the equipment should be easy to keep from freezing. One for a return fitting, and the other for a suction fitting or two. Did you say this was going in a cold climate or did I just assume?
It will not be in what most would consider to be a cold climate (Tennessee). They cabin is used sparingly in the winter time.