Ok, you already have two bulkys and 2-3 sweepers( is your breloom a sweeper?). I'd say go with a lead bulky, which means Donphan. If I'm not mistaken Donphan's only real lead weaknesses are LeadPert, which is quite rare, and Mamoswine, which won't OHKO with ice shard due to Sturdy. I'd use the following:
Nature- Impish (+Def, -SAtk)
EV's: 252 HP, 252 Def, 4 SDef/ 4 Atk
Strategy: You stated you wanted a Stealth Rocker, so here it is. Stealth Rock, to Stealth Rock. Rapid Spin to make sure your Houndoom/Gyrados aren't screwed over by rocks. Earthquake to make sure you can deal some damage before leaving. The last move is up to you. Toxic+Rocks will annoy your opponent to no end. Roar is beautiful when used with Rocks, and I'm sure that needs no explanation. Knock-Off is a great annoyer to get rid of the enemies item. I prefer Toxic, but like I said it's up to you. For EV's, 252 HP and 252 Def makes you the perfect tank. Then just dump 4 into whatever you feel you want.