Rust Between Bed Floor and Front: Mitigation?

What's the Line-X warranty? Maybe they'll do something.

I have used this with great success . It looks like weld beads more so than pads of any sort to me, even zooming in. You could use something like Naval Jelly to remove the rust, then prime it and paint it with a rubberized paint to match. Or try the Rust-oleum I linked to, and then use a rubberized paint. I used it on a quarter panel of an old Fury I had, Bondo'd and painted it, and there was no rust or rust bubbles showing 4 or 5 years later when I sold it. Lasted better than the other side that I sanded, primed, Bondo'd and painted; that quarter started showing rust again about 3 years later.