I have been playing around with your team and have had great sucess with it.
I know you said you chose Hipo over Tyranitar due to it's bulk, but I just saw this set in another RTM that popped out to me:
Tyranitar (M) @ Leftovers
Trait: Sand Stream
EVs: 252 HP / 176 SAtk / 80 SDef
Sassy...