I just noticed on the www.airstreamdreams.com
site that the flat piece I need is about the same price, but I'm going to go for the Lexan because of the breakability issue there.
I'm also going to not get molding because of the appearance.
Thanks for all of this help. When I posted first I was very unsure of what to do and now I can get moving with some confidence.
For everybody's info on replacing windows, the airstreamdreams site has a link to information on how to hopefully fix leaks and maintain existing windows on our 66 - 68's. It's got pictures and a great, clear explanation of how to and what to.
I plan to do some shopping there just because they provide this great resource, and because I MUST have some paraphernalia! I think I'm getting a teeshirt.