I run an extang Full tilt toneau cover,My fourth one since 97' ("tupperware lid", not snaps) and an extang maxseal tailgate seal, My truck is in the car wash at least once a week and my tools remain dry, hell I get more water through the sunroof from the force of the carwash if I forget to pull the sunshade closed than I get in the bed! I'm terribly impressed with extang's customer service so I keep buying their products here's the link to the maxseal, but there are a lot of similar products!
Has anyone come up with a trim kit that has a heavy rubber seal that will properly seal the rear gate. Now that I have a nice cap and a bed liner it would be nice to have a seal to prevent dust into the bed area. So far, I have not come up with an adequate seal.
I have a 2013 SCAB XLT 4X4 with a Leer cab high cap. I used home weatherstipping (like you can get at Lowes, Home Depot etc) to seal the tailgate. Two sizes had to be purchased based on the size of the gap at the bootom and up each side of the tailgate. This is the same approach I used on my Dodge (it lasted 10 years). Another major source of dust being forced into the bed is the set of three holes on each side of the bed just inside the tailgate that I believe is for the Ford cargo holder accessory that you can have installed. I pluged all six of those. If you check under your bed you can see the dust is almost funneled up openings under the rear corners of the bed to those six rather large holes. It has worked well for me.
I also noticed dust just inside of my tailgate and it comes in from a seem in the sheet metal behind the wheel wells. No idea why that is not sealed up but it takes in dust from the rear wheels. Will likely run a bead of silicone in from the underside to seal it up. Attached pic does not show th dust real well but you can see the seem that runs across the rear corner just forward of the tailgate.
I got my seal the other day at Lowes. 3/4" x 5/16" weatherstripping for doors. It worked well for 5 years on my Dodge and I don't see any reason it won't on this one. Best part is that it was all of $5.95