I used the 1/2 inch 3M double faced,,, I believe there is only one kind,,, and it has been holding up well so far. As far as keeping water out, I don't really think it is that critical, in making a watertite seal. I could be wrong, but my wagon has been loose for a couple of years before I decided to fix it and I know there are no issues related to water in the front section of the car. God knows I have had it torn apart enough times to see.
