It should work OK here. With the engine and exhaust manifold heat, I figure it will help as well. I am sure that in the Great Frozen North it'd be a challenge to heat that uninsulated cab anyway...
At todays temp if about 35F it was plenty comfy in the cab even at 45-50 MPH. How the defrost will work is still a guess though, and if its like most early Jeeps I've driven, it'll probably be marginal anyway. I don't expect much in that respect.
Just so long as my toes aren't about to drop off that's good with me.
"Free advice is worth what you pay for it."™