As some have pointed out before, and i noticed starting on mine, the trim around the rear wheel well and where the door closes traps water and i think the way the trim is designed it wears into the paint, causing rust. if this gets too bad it can eat into the weld between the inner and outer body panels, cause the whole area to rust out.
I checked my truck and sure enough that area was starting to rust, not too bad, but starting and i could tell was going to get worse. so I decided to try some preventative action. it may not have been the best most complete job, but it sure makes me feel better about it.
basically i just removed the trim and sanded down under it where there was rust to the bare metal. cleaned it up, primed and painted. it actually was much faster/ easier than i thought it was going to be. I DONT THINK that the rust started to get in between the panels, but its possible. if it is, well i dont really have the means to do anything about it at this time, so im going to keep an eye on this area and see how long my fix holds up, if i see rust coming through the paint again maybe something more intensive will need to be done. Im trying to keep this thing relatively rust free!
anyways, I def recommend just checking your truck and see if rust is developing, and decide if you want to do anything about it. luckily for me the white of my X matched pretty well with regular ole gloss white enamel, others may have a harder time finding a good match, but the area is only visible when the door is open, so you could paint the inner fender area flat black or gray or something and it wouldnt look too bad.
Before: the driver side was about the same condition and got the same treatment.
After about 10 minutes of grinding and sanding, I did more after this pic and before painting to try to get as much rust off as i could. yes my grinder got knocked off track and dug in at one spot, .. oops.
Taped off and primed
first coat of white, i did a second as well
all done! just gotta let it dry
I ordered this replacement trim on amazon, looks like it will do the trick, I cut it to lenght matching the old ones. my thought though is, should i just leave it off? it seems to me like the trim is the reason that the rust started there, so maybe its better to leave it off? the door has its own seal anyways, and the whole back side of the door isnt even really sealed, which is how water gets in there in the first place.. i have to let the paint dry overnight so im leaving it off until then anyways.
Paints used were Rustoleum self etching primer and rustoleum gloss white enamel.