I’m sorry John, but what do you mean by inside? To my best knowledge German wartime planes only had fabric in the moveable parts, like aileron, ruders, etc, and even those sometimes were not fabric made.

I recall the Henschel 123 as one of those pre war designs that soldered into WW2 having the rear fuselage covered with fabric, and some even with wing fabric. I confess the Arado 196 completely slipped my mind.

The only references I have about fabric protection coats are described as Cellesta dope, or more commonly named base coat red were the pigment iron oxide present, and 2 others: the aluminium bronze pigment that was used in silvery paints and a light grey that derives from the Cellesta but not having the iron oxide added. At least this is my interpretation.

These infos I got them from Michael Ullmann’s “Luftwaffe Colours” book.

Hope this might help but I’m sure someone out there can be if more precise assistance.