Scott,
It's held up beautifully. It is still lying flat even though it is not fastened down at all. Just seems to stay flat under its own weight. Of course, we'll see what happens as the coming summer humidity rolls over it.
Were I to do it again, the only thing I'd change is – fewer framing members. The rows of holes that straddle the "stretchers" keep the clamps from rotating 360º. Those extra cross braces were included on the theory that the lag screws that protrude from their top edges could be adjusted up or down as time passed to counter the top sag or bow. (You may have to review the photos to remember my "Rube Goldberg" adjusters.) However, I haven't needed to adjust them yet so they're just "semi" in the way. Of course, there are other holes to choose from. What I'm going to do is somehow mark those rows of holes on the top itself or on the holes' inside edges so I can readily identify them.
Thanks for the inquiry. Joel
