I've lived in Montana for 30+ years and heated with wood the entire time. Installed 4 woodstoves during that stretch [three in mobile homes] and have always gone with the Canadian-made double-walled stainless lined stuff after learning from the mistakes I made in the first one when I used single wall cheap black hardware store pipe inside and insulated Metalbestos exterior chimney pipe..
I had a controlled chimney fire about every two weeks in the winter in that installation due to the rapid creosote buildup caused by thin, cold pipe/resinous woods/oxygen-starved smoldering overnight fires/no rain cap. I would build a quick, hot fire with paper, cardboard and pine cones and get that cheap sheetmetal stove glowing red. The glow would begin to creep up the pipe and a faint roaring sound would begin. I'd step out the front door and see an orange tongue of fire maybe a foot tall coming out of the chimney [always made me think of the Day of Pentecost for some reason]. It would only last for maybe a minute then die out and my chimney was clean!
Of course, that pipe only lasted about 2 1/2 years, then I replaced it with the good stuff and the Pentecostal shows became a thing of the past...
What I've been told by the local stove places is that you should NOT stuff that 2" airspace in the support box/thimble/whatever it's called in your neck of the woods with insulation.
The insulation WILL eventually physically conduct enough heat [if you're burning 24/7] to the opposite side of the airspace to slowly begin to turn the wood framing surrounding the thimble into charcoal. Should you have a chimney fire with resultant higher than normal flue temps that charcoal can ignite at a pretty low temp and presto!-you're buying a new roof if you're very lucky.
If you're not so lucky the charcoal conversion process continues until the wooden framing eventually has no mechanical strength remaining and the chimney collapses and probably sets both floor and roof on fire simultaneously.
