I just bought aluminum 6-32 nut certs from McMaster Carr. The wide ones are made for thicker material and have ribbed edges to grip the fiberglass. The skinny ones are shorter pull and I used those mostly in the aluminum bits under the back of the car.
So you didn't use the slotted ones like I posted that flair out into an "X" like a hollow wall anchor?
i also thought about using well nuts by I figured the rubber head would be enough to cause a leak in the leather gasket.
Which reminds me, I assume you got yours sorted. I was going to post (before I saw that the thread list was a couple of years old) that I'm going to use several slatherings of mink oil waterproof shoe dressing before I install it. I figure that will be waterproof enough for a convert with no top or windshield wipers.