I have recommended your spreadsheets on several occasions, both for transmission lines and for bass-reflex cabinets. They have been especially helpful to people who wanted to build a loudspeaker from my plans, but with some cabinet modifications. If they intend to make a tower, I frequently suggest they check the impact of their modifications using your bass-reflex spreadsheet.

About insulation, I don't think that myth is limited to builders of bass-reflex speakers. I've seen it coming from several sources. We've all seen people talk about lining some part of a cabinet with felt, or something else thin like that. But the best place for an absorbent material is spaced away from the boundary, so a thin sheet would be best hung, suspended inside the cabinet. If attached to the wall, it doesn't do anything.

Wayne