I replaced both of my 3 step units with quad steps on my 2012 Sierra 365saq. It wasn't hard at all. I bought Stromberg Carlson quad steps from etrailer.com. I liked those because the steps had a radius like the original ones, and they had the antiskid material on them as well. If you search the forum for my screen name and steps, I am sure you can find pics I posted. I will look as well and respond again with the link if I can. I has to cut the skirting on my trailer just a little, maybe 1/4" on each side of the stairs, tin snips worked great. The upper bolts (which on my unit come through the finished floor, so all you see is threads matched up just fine. The back braces though, I had to drill out. I didn't drill the farm, I drilled the steps to match the holes. Worked just fine.
Loving our Sierra 365SAQ
Nights camped so far in 2016 = 0
Although Many trips scheduled.