Dragon Pulse has another interesting property of being able to hit Rotom-W for at least something in rain.
252SpAtk Flash Fire Heatran (Neutral) Dragon Pulse vs 184HP/4SpDef Levitate Rotom (Neutral): 32% - 38% (93 - 110 HP). Guaranteed 4HKO.
Otherwise you are pretty much completely walled, with Fire Blast doing half of that 50% of the time and HP Ice doing even less. Of course this isn't exactly an optimal situation but I find it happens a lot when I use offensive Heatran in this meta.