Guys,
I used a simple rubber product for the 'anti-squeak' between cab floor and rear cab panel. It is entirely impervious to water and if you use a thin but firm type, it wont compress at the area around the tightened bolts. I found a product that came in both a strip and an identical thickness but in a sheet. The sheet piece is ideal to cut the curved parts at the corners.
See here (I hope):
http://www.mapleleafup.net/forums/at...0&d=1330768164
Water or moisture probably wont get near my cab, but if it does, the rubber wont absorb it. I'm not sure of exact composition, but my original anti-squeak looked to be a canvas material containing a tar like substance. You can still get this, of sorts, from some of the vintage parts suppliers. For example, macsautoparts.com have this in several widths. It is "Frame Webbing (anti-squeak)" ,and is described as "oil treated fabric". They also sell "Body to Frame Welt", with or without adhesive backing. I did not use adhesive when I made mine.
Macs Auto shipping costs are quite high, be warned.
As Tony said, a good set of circle punches in various sizes, is a great investment. You will be surprised how often they come in handy!