So as usual I got under the truck for a small job and found five more to do. This one has me a little concerned though. I found the front most cross member that supports the bed is rotting out. I poke open two large holes on either end of the cross member near where the frame rails run. Also, the middle of the piece feels a bit squishy. The other cross members seemed fine.

I don't usually haul much in my bed, but I am not comfortable with ignoring this. The question is- can anything be done about it without removing the bed, which is simply not an option for me right now. It looks like it attaches to the frame, bed, and sides of the rear quarters (in two small places) Has anyone ever tried to replace this part with the bed still on? Or- should I consider cutting out the rusted parts and welding in steel plates? This will be difficult since I'd be upside down and there is little room to work. I have pics of the spots below.

I have found the replacement beam on NPD, it is a bit expensive at $100. Alternatives would be cutting one off at a junkyard (still likely not easy) or fabbing a piece from steel channel. Thoughts? I hate to do a ****ty job and have to redo it later, but I will not be a position to remove the bed for several months at least.

Here is a link to NPD part:
National Part Depot- F-010610-4B

 

I would wait until you had the time to take the bed off , that would give much better access and ability to fix correctly.

 

I fixed the same one on my 79 by leaving the bed on. Just replaced it with one from a junkyard down south. Was about $100 or so shipped but it wasn't too bad to do and the bed remained on the whole time. I do have a 6" lift and 35's so that definitely helped in my favor

 

So it is possible to cut out the old one and slip the new on place? I didn't think it could be done. Also- is the piece bolted or welded into place?
If it can be done this way, then the only other real question is whether the bed floor above it is acceptable...