Neither would I, but I would put one inside a shelter like I've described, with a plastic sheet between the fire and the interior of the shelter.

I agree that you shouldn't "need" a fire at all, but the tent I made is lighter than any tent its size I've seen and it works wonderfully well with a campfire. The lean-to in the video isn't near as light as my tent, but it would work pretty close to as well for retaining heat from a campfire, and protecting your bag from sparks.

Since the OP's brother likes using a lean-to with a campfire the solution I offer is a viable option for them. It offers protection for his bag and a warmer shelter for their winter camping. Winter nights are long and cold and dark in MI, so I think it's a very good option.

I'll also add for clarity that it only takes a small fire built with sticks less than 2-3" in diameter to warm a "Super Shelter". You don't need a rip snorting, ember popping fire, and you don't keep a fire burning all night long just because you're using a campfire tent. You warm the interior of the tent and your sleeping bag inside it before you crawl in for the night and let the fire die down.

I have to add this: It's backpacking. If I had to worry about handling a WM bag in a delicate manner, as compared to any other bag, I wouldn't own one.