Air Sealing the Cabin

[RoundTwo]

As my interior renovation has moved from the deconstruction phase to making forward progress, I’ve run into a difficult area to seal up and am curious what others have done. 
While taping and caulking all of the minute little holes and cracks is being done, there are two huge holes that seem to be ignored because of difficulty. The problem is at the rear intersection of the steel tube cage and the airframe. There’s a direct passage on the outside of the steel tube and the skin that is open to the space below. The space below is to the outside of the rear seat pan, adjacent to the third row of lightening holes. 
Has anyone found a clever way of sealing this area up? It seems silly to be spending so much time on the little stuff when this area, one on each side, remain unsealed. 

[GeeBee]

If it whistles or lets water in, seal it up, if it don't let air flow and keep and condensate to a minimum. Never looked closely at other models but I actually have louvered vents coming out of my baggage area.

[RoundTwo]

56 minutes ago, GeeBee said:

If it whistles or lets water in, seal it up, if it don't let air flow and keep and condensate to a minimum. Never looked closely at other models but I actually have louvered vents coming out of my baggage area.

That’s interesting. Just about every seam and lap joint in the hat shelf and baggage area was sealed with duct tape, presumably from the factory. A lot of effort went into sealing seemingly small sources of air, but this large gap was left open. However, a large majority of the tape had lifted and was no longer providing any sealing. 

[GeeBee]

I circled the louvre vent. It connects (but not directly) to an inside vent.

[A64Pilot]

All I can add is be careful what you use to caulk, some like silicone are actually very corrosive to aluminum, that vinegar smell, it’s is actually vinegar pretty much and vinegar is an acid.

[Skates97]

Some Super Soundproof closed cell foam insulation, cut a little oversize and stuffed in?

https://www.aircraftspruce.com/catalog/appages/supersoundproofsheet.php?clickkey=59594