Buck-naked / butt-naked
Here’s the straight dope: when you step, you are setting your foot into a new spot. So … It’s either “set foot” or just “step”, it’s superfluous to say both in the same expression.
As for rash if shit, never heard if it. But it’s most likely ration of shit, meaning portion or piece, as in piece of shit. Rash means a rash on your skin.
Lastly, for all intents and purposes, I hereby also confirm that this post is not for all intensive purposes! 
Set foot all the way. 62, lived mostly in Ohio and Maryland.
And in Maryland, “raft of shit” was the way I always heard it, back in the 70s.
^This
I have never heard rash, ration or raft in that manner, but could it have originated as “rasher of shit” as in 'rasher of bacon" - meaning a thin slice? I mean, what is a proper ration of shit anyway?
I see/hear both, but would only say, “set”.
But at least “ration of shit” makes sense! I’d never heard that one, in either version, so I am fertile ground for this kind of error. (Thanks for the warning!)
“Chester drawers,” at least, is funny!
I think I’ve heard both but I say set foot. Also, include me in the group that says ration of shit. I’ve lived in Washington state all my life, and am sneaking up on 50.
After six years my never-thriving then long-dead thread arises. It Lives!!! Sniff, sniff. I’m so proud. My first little zombie. {hug}.
And in the intervening 6 years I still haven’t heard “step foot” in person. Just written on the 'Dope from time to time.