Don, your stanchion/post is hollow is it not?

Make up a threaded weld bung with a step and JB Weld it in place from the inside.

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The WW pivot nuts don't fall off because they're nylocks and also because when they get loose - from swinging the WW's in or out - they'll drive you nuts and you'll torque em back to where they should be.

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The Lexan rear quarter windows are secured to the oak bow and stainless top iron piece the oak bow is on.
Slightly longer stainless sheet metal screws into the wood and an 8-32 allen with nylock through the oval hole at the bottom.

Since the quarter windows are supported only in the middle you need a fairly sturdy thickness of Lexan.
I tried 1/8", but they fluttered/buzzed at highway speeds much like the control surface in an airplane will when max speed is exceeded.
3/16" stopped that.

The quarter windows do well in keeping the wind that comes off the windwings from curving in and hitting short passengers right in the ear.

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One thought I have about side windows is a sheet of 3/16" lexan on a hinge that mounts to the top's horizontal bar above the door.
An over-center spring setup to allow the window to stay up or down would help.
Granted, it would leak air to an extent, but the main thing is rain would stay out of the cockpit for the most part.

16 degree's F is my personal best in the roadster, but below freezing at highway speeds can get a touch chilly.

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A couple of pic's during the quarter window mock-up phase.
They will impinge on the ingress-egress bit, but not bad.





Note the notch for the main top bolt, not used for the quarter window install.