Sealer for fender to inner fender.....

The factory used dum dum, it's a gray putty like substance you can get it at any camper parts dealer. The factory used a caulk gun to apply it but I got a role of it that was 1" wide 3/16" thick and the role had about 25' on it. I just cut it to fit the area and stuck it on, it went on easy and looked great.