To be honest with you, Heatmor is more of a Special Attacker, thanks to it's Bulbapedia Page. I would suggest to ditch all of those moves and have a Special Attacking Moveset instead.
- Inferno/Sunny Day
- Focus Blast
- Solar Beam
But if you want to keep that set as it is, I would go for Low Kick to help it's Rock weakness.
Hope I helped! :D