Love your Sun-team and your presentation! It makes me want to start playing Drought again MHMM.
Anyways, I agree with at least testing Chlorophyll Tangrowth. It's incredibly bulky on the physical side and will take on the priority fighting-type moves that Heatran hates. Give it max Speed and a set of Power Whip / Hidden Power Fire / Growth / (Earthquake or Rock Slide or Sleep Powder or Sunny Day). I think you might be pleasantly surprised by the results!
If you opt for Earthquake on Tangrowth, it can take on Heatran after you sac a Pokemon and OHKO. Then perhaps you could put Sunny Day Espeon with a Heat Rock on your team? That would alleviate Stealth Rock for the rest of your team while giving you an answer to Thundurus. But whatever you decide upon, I think that this team PROVES that Sun-based teams don't need Rapid Spin support. Methinks our playing styles might be a little similar, and I can relate to the idea of not needing one. Your goal isn't to switch around a whole bunch. It's to dent huge holes with Fire-type moves under Sun to win the game. So absolute congratulations on that.
I dunno, these are some crazy suggestions that probably aren't optimal. You seem very set with your team. Kudos!