if it was me i'd probably get it down to bare metal where the rust is, put some POR15 black on (dont get that crap on your hands it lasts a week lol), repaint, then put the flares on like someone mentioned.
I`ve got an 02 quadcab, the only rust on it so far is under the extra chrome strip I put on the bottom of the taigate, using pop rivets w/ no sealer on them. no bed rust at all-????????????