This may sound unorthodox, but I did not glue mine down. I cut my own mat to fit snuggly between the chrome rails so it doesn't slide or bunch. I "open and inspect" underneath the mat every now and again to make sure nothing bad is happening under there. At least this way I know that no stray moisture is building up and doing nasty things to my door sill.
Steve Iatrou
Seaside, CA
1964 230sl roadster
White (050)/Black (116)