Here's more photos.
The first two confirm that the faces of the spar in the wet bay were coated, as well as giving a good look at the outside of the wet bay faces of the two shear beams showing that they were too.
The third photo is inside the cabin and the freshly primed area along the lower wall is where the rubber there was removed.
The last one shows the underside of one centre section as recovered. There's no sign of covering, however there is also no paint as the a/c that came from had been returned to natural metal and the Hudsons had been replaced by Venturas so it may have been deemed redundant to leave the exterior coating.
My estimate of the thickness is somewhere between 1/4" and 3/8".