There isn't a way to seal that up?
If you seal it up then after a very short time you can’t see thru it, it also holds ash in the tube. You need an air wash of some kind in a view port to keep the glass clean and cooled somewhat.
Since the G series uses a power draft and they build quite a bit of vacuum, it will actually pull the door shut on the G400 if you just crack it I made a prototype that did shut off when it idled and only allowed air in when it was running, glass would be black by the next morning from the combustion gasses present even during a idle.
Basically used some very light springs to push the glass against the outer plate, I had ports milled into the thicker piece that held the springs, when the stove started it would pull the glass away from the outer cover which allowed air to flow around the edge of the glass. It did work as creosote was decreased, but the daily cleaning of the glass wasn’t worth it.