I'm currently testing a new sealant for my wood stove pipes. I think, in retrospect many of the issues comes from the bend, the elbow. But by doing it this way, my roof stays in tact, with no leaking issues.
Still, the window option is working, but a little more fanaggling.
If the heat on these pipes is a little intense, then I let it cool a bit before adding more wood. Its pretty fast.