Like Platinum said, Wash Rotom is better using a physically defensive set. If you really wanna use an offensive set, this'd work better than what you got now:
-Rotom-W w/Leftovers or Sitrus Berry
Nature: Modest
Ability: Levitate
EVs: 232 HP, 56 Sp.Attack, 220 Speed
Moves: Volt Switch/Thunderbolt, Hydro Pump, Will-o-wisp, Hidden Power
If this is a PokeBank team, consider this as well:
Skarmory doesn't need both Spikes and Stealth Rock, especially since it likes to have Roost. So switch one with that. Heatran also doesn't need 3 fire attacks. No Pokemon does. It just needs one fire attack: either Lava Plume or Fire Blast will do. It's other moves should be: Earth Power, Dragon Pulse, and Flash Cannon.
If this is not a PokeBank team:
Tyranitar or Hippowdon should be your Heatran replacement. Skarmory, Excadrill, Gliscor, and Mega Mawile aren't negatively effected by its sandstorm, and Rotom (if going the defensive route) doesn't care much about the sandstorm. If running Tyranitar/Hippowdon, Excadrill should have Sand Rush as its ability; an Excadrill in the sand with Sand Rush can be beastly.
Finally, I wouldn't recommend basing a team around Haxorus. Like Hydreigon, it took a nasty hit from the introduction of Fairies. The idea behind Haxorus is almost always SD/DD/Choice Band, then spam Outrage. Which no longer works with Fairies skipping about.
Scolipede isn't a bad Baton passer (it's arguably better than Ninjask). But I think Tyranitar/Hippowdon works better for your team with all its sand-friendly Pokemon.
Nah ンン
“No, I... I have to be strong. Everyone expects me to."