[HO455]

Use a wire brush to remove as much of the rust as possible. Then treat with Ospho or similar product. Then prime and apply the seam sealersealer then paint. Most modern seseam sealers don't require printing after. You can use Por15 too but you will need to scuff the Por15 so your primer will adhere to it. I can recommend Sem self leveling sealer. I did this on my Burban. There is some more info on the first couple of pages of my WMB thread. (Link below.). Although my experience is the water from the drip rail goes down the A pillar and down behind the kick panels and out the bottom of the truck unless that is plugged then it rots the kick panel and floorboard. Unfortunately water in the glove box usually comes in from the cowl or window seal being rusted through
Good luck.