I used a CRL product years ago. Use to be step by step by myself and others with pictures on how to repair your windows using the CRL window products. It is a double side close cell tape and a sealant to seal the window after you took it apart and clean it and put it back together. I can no long see it here so must have get dump over the years. This was back in mid 2005. I did all the windows in a Newmar and just saw it the other day and they still look good and are holding up. MY windows were 1/4 space between so I use the 1/4 tape.
superspacerthis is what I was looking for
windows crl part number