I'm afraid the silicon bronze isn't an option for me. I will be spraying DPLF90 in the next day or so, but I just don't know if I should do something to the seam prior to spraying. Is that seam sealer flexible at all?

As for the driprails, are you saying I should use that seam sealer to fill in the rails completely or just try to fill in that body seam down in there? If you are saying that I should just try to seal the seam, it sounds like a difficult task. I have to fold sandpaper around a puddy knife just to get in there to sand.