Lots of questions coming....
When you 'dope' the cloth, is the protection just on the outside of the fabric surface? Or is the fabric itself protected, thus meaning the string of the fabric absorbs the 'dope'? (Going down to the micro-scale of the material)
In your explanation of the airplane, IIRC there is an inner frame with outer cloth that tightly fits across the frame. With the fabric condensing on the frame, not only does this add structure and stability to the frame, but the 'string gaps' in the fabric become lesser. With the gaps lesser, the airflow is limited to go across the fabric rather than through it. Same with water.
My understanding of your canvas use was to use a lightweight frame, interior lined wood paneling, and a fabric exterior. No mention of insulation or treatment of the lightweight frame or the backside of the interior paneling (I'll assume the floor would be treated).
In building a TD, most use solid sides so side insulation is none or it's added to the inside of the exterior wall before the interior panel is installed. If there is a frame for the sides, insulation is placed between the frame rails and secured to one of the inner or outer walls. For the top of the TD, most have crossmembers, insulation between the crossmembers, interior paneling, and an exterior panel that is aluminum or wood that is thin enough to bend to the curves of the top configuration.
With the insulation, not only is the temperature somewhat controlled, so is the noise. When doping the canvas, and the effect on the canvas is to shrink, does this add a R-value of insulation to the fabric? I would tend to think so.
Here's a thought, have separate sub-frames for floor, walls, top, front, back, etc., canvas the separate sub-frames, then assemble the TD? You encompass the frame on both sides with the fabric. Edge trim could hide the assembly screws/bolts. That would be cool.....