As Waffle says, I textured it as bare metal. I recall spending a long time researching what colour the various interior parts of the B-29 should be, including going through the painting instructions on the original maintenance manual for the aircraft. Bare metal B-29s had bare metal flap interior skins, but offhand I can't remember whether I researched whether the OD ones had bare metal or primer there. If anyone can provide proof it should be primer I will change it when I get time.
