So a couple months after I got my 04 FX4 I found that there was some hidden rust underneath the factory bedliner... The salt from this rough new england winter didn't help it, as it has gotten worse since the pics were taken (You can see both wheels clearly through both sides from the top now.) I had a body shop look at it and they quoted me $1000-1200 to repair it. Plus another 5-550 to Line-X it. I really would like to save the bed because other than those 2 spots it is mint as you'll see in the photos, and even the underside supports are in good shape... I have looked and looked online for the forward corner pieces to cut and replace, but to no avail... Would anyone have any ideas I may have not thought of?
Here are the pics...






As you can see from the photos below, the rest of the bed body is in prestine shape... Help me save her before its too late! lol

 

That sucks man, I am in a similar boat with my cab corners though . Sucks that a 10 year old $45k truck has so many rust problems. I wonder if my bed looks like yours could you see this from underneath?

 

If you have a plastic bedliner , and you've never removed it and cleaned under it, there is most likely some rust under it. especially if you're in a snowy area... You can feel it from the outside but its tough to see because its hidden by the wheel well... carefully feel just behind the wheel well and up to the bed floor... thats how I noticed it... If you have no rust you're lucky, and if I were you I'd rip the plastic liner out, throw it away, and get the thing Line-xed... This isn't a Ford issue, It's a Bedliner issue... Those things will eat any truck...

 

the truck is nice enough that I would repair it.

 

Try to find a bed in your area (junkyards) that have been hit on its sides, but has a good, solid floor to use it as a "donor". Then you could have the sections cut out for a good welder to replace your rusted sections, then prime and paint. This would be the cheapest way to go, unless you could find a complete bed in great shape, and in your color.

 

I'm in a similiar position with mine except I never had a bed liner. I must have put a small hole in the bed and it has recently rusted through this winter, I'm gonna pull the box this summer and cut the rusted section out and replace it. What would be the best size thickness to use as a patch?

 

Get a good used bed.

 

Best idea, but locating one in his color in great shape will be hard at best.

Buying one with a good inner bed, and banged up outsides will be cheaper, as he can cut out the pieces he needs, weld in, then paint just the floor. Better yet, get the new floor surfaced with a good quality bedliner to prevent future rust.