I have a 642. I put a drop of Break Free on a patch and use that to wipe down the exterior of the cylinder, barrel, yoke, trigger, and cylinder release latch, followed by a dry rag. I do this once I've finished cleaning and lubricating my gun, which happens about once every 1-2 months or after every range session, whichever comes first. At the end of the day (or sometimes twice a day if it's really hot and humid), I just do a quick wipe down with a dry rag. So far I haven't had any rust issues.
Personally, I'm not sure I'd wax a gun, either blued or stainless, that I'd be using as a carry gun. To me it seems like too much trouble for a gun that's going to be seeing some wear anyway. When I had blued guns I used either a rag with some Break Free on it or a silicone rag to wipe them down periodically and while there was definitely finish wear, there was no rust.
The only reason I can think of for using wax on a stainless steel gun would be if it had some kind of special finish that you wanted to preserve, i.e., if you had a matte or frosted finish but didn't want your holster to polish wear lines on it.