Pocket, I disagree with Scarf being so far down. Scarf is definitely among the best Heatran sets atm. Not enough people prepare for it, and once rain is gone from the opponent's side of the field, they might be finished. Heatran's largest issue is Speed, and Scarf fixes that. Not to mention, Heatran is an excellent revenge killer with its typing, coverage, and power, which few other Scarfers have. Heatran is an excellent cleaner, especially in sun. I would say it competes with specially defensive for being second in the set order. Generally, Choice Scarf Heatran is a great anti-meta Pokemon. imo, offensive > choice scarf > specially defensive > weather trapper > choice specs.
A couple things on the specially defensive set: First off, Stealth Rock. Heatran is an amazing Stealth Rock setter. It has the resistances, the bulk, and the ability to force switches if your opponent doesn't know which set it is using. However, Stealth Rock + Roar needs to be possible with that set. Also, Roar is definitely mandatory imo; otherwise, Heatran can't deal with stuff like CM Latias, SubCM Jirachi, etc. On a more defensive team, sure, Toxic is great, but offensive teams don't necessarily need Toxic. Also, I don't get why you need Will-O-Wisp; Heatran fares poorly versus most physical attackers and can spread burn with Lava Plume regardless. I recommend moving it to AC. Also, Protect doesn't need to be mandatory. Heatran can live without it. With that, here's my proposed moveset
move 1: Lava Plume
move 2: Roar
move 3: Protect / Toxic
move 4: Stealth Rock / Toxic
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