You did say "bare" metal? I por-15 the window openings and then painted them. The design of the side windows should allow any water to drain into the collectors. The channels are stiff enough, plus the glass and trim mldgs hold everything in place, right? I just don't think it is designed to be sealed. When I cleaned up my burb windows I didn't notice any glue or sealant in the window openings. Maybe after 50 years all evidence is gone? Hopefully someone with more burb knowledge will see the post.