I made a similar team some time ago but as I'm still not very good with this I'll ask again for help:
I've got this sandstorm team:
It works good in most cases, I've got Hippowdon for sandstorm and rock traps, and then I go on depending on the type of enemy I go against. So I need to have viable choices to that last spot, and I wanted to include a rock type just for the Sp. Def boost the sandstorm provides.
Some of the candidates are Mamoswine (For the Physical bulk and Ice cover), Cradily (Rock type for the said above, plus its Storm Drain + Sludge wave totally saved me agains Amaria) or even a defensive Mega Steelix... Or maybe It would be better to just keep Sp. Atk Lucario or Physical Metagross there, but I fear that would leave a lot of weaknesses or slow mons...
When EP18 comes around, I'm going to get Tyranitar for sure, but I will probably intersect it in another mons' space.