I recently purchased my 2002 F350 PSD as a used unit. It was very clean and spotless. It also had the stainless Steel trim in the wheel wells. Due to my past experiences with rust I decided to take them off as this was a new enough truck and hoped to prevent rust. Much to my dismay, the paint was bubbling around several screw holes. I took it to a body shop and had the box wells repainted after they welded the hole shut, as they were the worst. The bubbles actually went around the lip and started to get into the box sides. The front fenders were ok except for 1 screw hole that is bubbling on the lip only. I ground it down to clean metal with a dremel and a wire wheel. I then touched it up with touch up paint. Anybody have any ideas on how to stop the rust dead in it's tracks? I thought about rubbing regular grease around the inside lip, but would this hold moisture?
Any ideas is appreciated. This truck only has 39K and I want it to last 8-10 years.
Also, anybody with those stainless steel fender trim should pop them off and take a look at it, you might be surprised like I was!!

 

Get hold of some rust bullet. Rustbullet.com
This stuff works for me its miracle paint....

 

By having the holes welded up you may have just created more of a rust problem than you had to start with. The heat from welding will burn the galvanize, primer and paint off the inside of the box lip. Bare metal will start to rust in a very short time. "Between the inner wheel well and outer box side, can't be seen." Make sure to get some undercoating on the welded areas ASAP.

I use heavy wheel bearing grease around drill holes to help fight rust, after zinc primer and paint. Grease will not trap moisture.

 

Anytime you weld, you need to brush/grind the junk off and paint it. I was welding my mesh trailer decking in fall and forget to paint it that night, the dew overnight had it all rusty till i got home from work the next day. If dew can cause that, imagine what some rain or road salt will do.

 

Chipper,
The body shop did spray undercoating on the back sides of the lip. But I know how well that holds up. It is already peeling off. I was curious if the grease method has worked for you as you are close by me in the "salt belt". I just figured that none of the grease fittings or gears on my JD snowblower have any rust on them, but I grease them annually before snow falls.

 

so2315
You need to get some rustproofing on the backside of the boxside. Into the "inside" of the lip. This area can not be seen. Use the runniest undercoating you can find. So it will "flow" into the inside of the lip to protect the welded area. This should be done anyway if you plan on keeping the truck for a long time.

Road salt, dirt etc will pile up in this area and hold moisture, causing rust. This is why you see most trucks rusting out along the boxside wheel well areas. Now that the factory rust protection has been burned away you will need to watch this area more closely.

Hope this helps.