Robert,

Have you ever tested an SOF for flexibility before and after the skin is on?
I have and the difference is not much - noticeable but not a large change.

Your story about the coating penetrating evenly is wrong.
Some places in the middle of the fabric I can see "runs" of varnish on the inside.
If it penetrated evenly, why won't the frame have the same color everywhere - the darker color where the finish penetrates? If I could get even color over the frame I would be happy.
Breaking the bond where the color is darker tells me the penetration is not uniform, because where there is no dark blotch the skin separates easily. So there was no penetration.

Byron, thanks for the report about Linseed oil and no blotching. Normally I have a prejudice against oil, but whatever works.