Jim ,I don't think the sealing has to be extreme. And only extreme treatment I've seen In this thread is in Alaska. That's where
they use dogs with extreme fir.
MDO mfgs say edges need to be treated. But I've seen plenty that are not treated. Mfgs want it ALL treated. I see
no reason to think EXTERA needs more treatment than MDO. An easy extreme treatment would be Titebond 2 brushed
on edges ,press down strip of canvas , let dry ,trim with utility knife. It will make ordinary ply wood as weatherproof as
MDO.