I would run hp grass on him, but then how would I handle abomasnows and ferrothorns. Btw, I have no problems with gastrodons, since latios can take it down easy.
Metagross and Zapdos can respectively counter their mirror matches. (Abomasnow/Ferrothorn).
Hp grass allows you to keep your Dragon gem and counter other Rotom-w who use Hp fire.