Nice team by the way, Life Orb Hitmonchan is beast.
I'm not too sure about your Sandslash set, however. You say it's pretty replaceable and I can see why; defensive Sandslash is really quite underwhelming. First off it gets destroyed by most spin blockers. Rotom can come in on the Rapid Spin, set up a Sub to block Toxic and whittle Sandslash away with Shadow Ball. Also, by running such a defensive Pokemon on such an offensive team doesn't make much sense; that 'mon is always going to end up lagging behind. That is why I suggest you change Sandslash to the mighty Swords Dance Sandslash. I've been runnning it for a while now and can say that it is really good.
Sandslash @ Lum Berry
Ability: Sand Rush (not that it matters)
EVs: 252 HP / 252 Atk / 4 SpD
This can lure in and beat a lot of spin blockers. Without significant HP investment Rotom is always KOed by Stone Edge after Stealth Rock (and even bulkier versions have about a 50% chance of being KOed). Spiritomb is slower than Sandslash and can't take two +2 Earthquakes. The same applies to Dusknoir and Cofagrigus. This set can still take a good amount of physical abuse thanks to full HP investment but obviously isn't as bulky as your previous set. No Stealth Rock sucks but as you said you rarely find an opportunity to set it up any way so you shouldn't note it's absence too much.