I'm not a huge fan of Hippowdon and Breloom. I think Dragon Spam is most effective when you go all out. Hippowdon is just too slow and defensive, and as a result, it's weighing down your team. I think you should try Mamoswine instead. It's often seen on Dragon Spam teams for good reason. It can use Stealth Rock, and since Dragon Spam teams tend to be weak to other Dragons, Ice Shard is invaluable. Mamoswine being much more offensive than Hippowdon will help you keep Offensive momentum.
Second, I think you should try out Dragon Dance Dragonite instead of Breloom. While Breloom is a great Pokemon in the current metagame, I don't think it works well with the rest of your team. Dragonite provides you with a much better mid game wall breaker. Take the chance to set up and then KO as much as possible. Dragonite counters will be severely weakened, and your other Dragons can take care of the rest of the match. ExtremeSpeed is notable too because priority moves are always important.