Someone earlier said that that sentries were a weak point in your build and I am not sure I agree with that. especially for a calamity user, they were dealing big damage at an incredible attack speed. You don't have any hatred problems keeping the sentries up and I am starting to think whether the 6s cooldown rune might be better than spitfire turret.
I agree, sentries are incredible. You may be onto something with the reduced cooldown rune, though I've always figured the 2 second reduction doesn't really warrant the rune choice unless I'm running Custom Engineering. My line of thought is that since sentries are taking advantages of all the damage buffs of mine, having spitfire rockets also getting those same buffs made it worth slotting. I'll definitely give the viligant watcher rune a shot though.
Your build will be really good with Bait the trap with the CC helping SoT but you likely won't have the disc. to maintain it especially for a kiting build.
I know!! I was messing around with bait the trap last night and it's incredible with this build. Unfortunately due to the amount of stepping, im never able to stand in one spot long enough, and not having any disc regenerators doesn't allow me to place a few of them stategically like I'd want to for it to work :(
Vault Acrobatics or maybe even using the Beastly Bombs rune instead might be worth a try in place of dark cloud...i'm sure some theory crafters out there can come up with something as well....but 712% over 12 seconds i.e. 66% weapon damage second for a skill that also target boxes doesn't seem to warrant a slot (for a slow manticore user maybe, but not for a 1 hander).
I'm not slotting RoV for the damage output here. It's for the snapshot utility mostly. The fact that I can have life steal for an extra 11 to 12 seconds without having to do anything at all is very useful in those crazy uncontrollable situations that ranged players often find themselves in (you can see this clearly in the mp 10 keeps 3 vid against the tremor pack) Also, RoV procs cold, so any time Im not able to shoot due to things like vortex, knockback, nightmare, etc, Dark cloud will still be going and provide a slow for me, allowing me to gain my distance again. The fact that it deals damage too is just a bonus.
I use to use either vault acrobatics or prep for a while, and ever since I came across life steal snapshotting with RoV, I've actually had an easier time surviving and even less dependency on shadow power. If blizzard ever do away with snapshot mechanics for DH class, I will definitely go back to using prep or vault.
As stated before, this is merely a preference slot. Most people will find vault, prep, or SS much useful and accessible.