Hey Paul those windows are still giving you grief huh? Where did you buy your gasket from? I have a small scrap leftover from doing mine that I can mail you to try if you would like. I bought it from Vintage trailer supply and they call it for the 1970's window glazing strip.
I have a small piece of broken glass in my car cupholder that came from my '69's rear window and it is only 1/8 thick but I know that window was replaced in the past so it may be not the factory original thickness, so when I redid my back window I used 1/8th tempered and the Vintage trailer supply glazing worked great. If it is just your front and rear window you are replacing at this point it may be worth ordering new thinner tempered flat panels. The side and wing windows on the other hand are curved and you will want to keep looking for the appropriate sized glazing strip as getting replacement glass for those is impossible and swapping out good glass for thin lexan would be blasphemy (not that you mentioned doing that)
1970 Airstream Window Glazing Strip