Need advice installing stepside fenders

[dave6672]

I posted this in the paint and body section and got a couple of good responses, but thought I might get a few more here.........Soon I will be putting my newly painted step side fenders onto my newly painted bed sides. Question - what should I put, if anything, between the fenders and the bed where the fenders mount? I'm talking about the flange that is around the perimeter of the fenders where they make contact with the bed. Some type of seal or gasket? Seam sealer? Or just mount them up as is? Thanks!