Ok, I have a 2003 Chevrolet Silverado 1500 LS with 220k miles on it. The body is in good shape, and with some work now, which I am in process of doing, will be in great shape.
As is pretty common, especially for those of us who live in rural areas, where gravel and, in winter, salt are kicked up by our rear wheels, the wheel arch portion of the rear wheels, is rotted out. It doesn't look horrifying, since the previous owner applied bedliner to the area. But that was already after the rust was there, and it only slowed it down. Now, I can literally put my hand right through it. It's just Herculiner there. In addition, I also have some dents and miscellaneous damage on the bedsides.

So here's my question: should I use these

which cost about $50 apiece, or should I replace the whole bedside

for $280 aside, not counting labor.

I am somewhat inclined to think the latter would be best. For these reasons:
1. You don't have to screw with cutting the appropriate portion out, and keeping it from warping while installing, etc.
2. I already do have other damage that would also need repair.
3. I want to refinish the whole truck, and replacing bedsides might be an easy way to knock out a large area of that (bedsides come with corrosion protection coating that can be scuffed off).
4. Even though you are working with a larger area, it might be a simpler process overall, making labor costs lower.

I say that (4) because I had the blacksmith, who I will ask about this job, replace the bed bottom for an old JD AMT 600. The reason I did that was because the bottom was rotten out but the rest of it was in fine shape. However, his time spent cutting and shaping and welding a new bottom in cost me $380. He told me that he could have built an entirely new bed for less than that, since it would have been simpler to slap pieces together than to screw around with removing the old, getting the new to fit and then welding it in. So, I kind of feel the same way here. It may be more expensive to go the repair panel route, than to replace the beside. Plus, I would still need to attend to my other damage on these bedsides I have.

Another question is what do you think about riveting a new bedside in, instead of use the spot welds. Would seem to do less overall damage to the new metal, drilling and riveting, rather than throwing hot metal around. Just throwing that out there.

I also have another truck with the sames issues on the wheel arches, but that one has $300 of Rhinoliner already on those bedsides, so I will definitely be using just the arch repair panels there, but there is no consideration like that on this 1500.

Let me know what you guys think.

Personally I would also go for the complete side panel, maybe somebody else will know how well they will fit but don't use rivets, for many reasons. To reduce the amount of welding, you might want to do some research on panel bond adhesive.

more than likely, once you take the bed off, you will find even more rusted out metal.
you might want to look into a used bed.

I've never used the aftermarket bedsides, but I can tell you that the patch panels usually require quite a bit of bodywork to get them to look right. Doesn't seem to matter where I get them from, they're all stamped iffy.

I would do the bed side. my boy and I put one on in about 4 hrs. with a lot of bsing and this being a new truck. the worst part is that you usually need to pull the bed back a little. i'm with tomsteve in that you may find rust at the seam, if it isn't bad you'll need to sand blast it. use panel adhesive to put the new side on, most go directly to CLEAN BARE METAL we also put couple good tack welds at the corners.
Jay D.

Yes, I was already planning on using adhesive. And I don't think the bed itself is in too bad shape, so I'd rather just reside what I have.

And as stated, I do lean myself towards new bedsides. I think, at least since there is other damage, that the rep panels would be an unnecessary headache.

Can you elaborate on the reasons not to use rivets?

I can tell you about rivets, I used them when I first started,
they always telegraphed through later on down the road.
I never figured out why.

I usually use glue, I use the small sheet metal screws to
pull the joint together and once set up I remove the screws and
fill in the tiny holes left behind by them with more glue.