Don't know if it'll work for a dually, but I bought a regular set of nerf steps, then a buddy helped me lengthen them. We also welded them to the frame, rather than the stock body mounts.
I bought these on amazon:
Stretched and installed
Close-up of the stretch job. It's not pretty, but it works. At some point, I might get them shot with Line-X or something similar, but for now I'm fine with them.
Nerf bars were welded to the frame. I'm having issues with my phone, so the photo's not well lit, but we welded a gusset on the frame, then welded square tube from that gusset to the nerf bars. The bars are rock-solid. Absolutely no flex. Each nerf step has three support tubes welded to it. I was a little worried about flex at the area that was stretched, but nope, it's solid.
I think the side steps were $300 on Amazon, I spend another $100 for the extra tubing, bought my buddy some adult beverage for his time.
G
I bought these on amazon:

Stretched and installed
Close-up of the stretch job. It's not pretty, but it works. At some point, I might get them shot with Line-X or something similar, but for now I'm fine with them.
Nerf bars were welded to the frame. I'm having issues with my phone, so the photo's not well lit, but we welded a gusset on the frame, then welded square tube from that gusset to the nerf bars. The bars are rock-solid. Absolutely no flex. Each nerf step has three support tubes welded to it. I was a little worried about flex at the area that was stretched, but nope, it's solid.
I think the side steps were $300 on Amazon, I spend another $100 for the extra tubing, bought my buddy some adult beverage for his time.
G