Hi Vance. Ya, I like the rubber-to-rubber idea. That should give you a little insurance. With Brent's approach where it's on a hinged/elbow type mount, it seems a swivel type connection where the disk meets the plunger would be required so the disk could flatten out against the seat. That may reduce the tolerances required. As you know, there's a million ways to skin a cat, and I'm sure both will work well with a bit of tweaking.
I love those machinist/fabricator type guys too. They always have good input on how a particular part or mechanism can be made. It's so important to keep an open mind, and consider advice from all sources. Especially when, like us, you're building a one-off thing that no one's seen before. I love this group of guys and would never have even attempted this little project without them. Looking forward to a few pics of your sub and related parts and pieces. I'm hoping we can get both our subs together some time soon. That will be a real blast. Frank D.