If you are looking to get some Dinitrol inside your sills, bear in mind that if you pull the plastic door plates off the car door sill you will see four holes you can squirt the stuff into. It looks to me like the sills have a third metal skin between the outer and inner skins. The door plates can be removed with a screwdriver carefully pushed underneath them to pry them up. There are three plastic attachments which push into three of the revealed holes. You might want to wrap something over the end of the screwdriver to protect the paint.