I'd definitely consider the lead that locopoke pointed out. Not only can it set-up Stealth Rock and the sun early on in the game, but it can also Explode, meaning you maximize the amount of turns of sun you can get without having to switch-out.
Your offensive synergy is very nice and well thought-out. Donphan is quite useful here, as it protects you against both Tyranitar and Salamence. However defensively is where you find some trouble. Often I believe you'll find yourself having trouble with heavy offensive threats or full-blown stall. With Spikes and Stealth Rock possibly on your side of the field, you team will face trouble breaking opposing defensive cores. Mixnape helps in this regard, but still leaves you succeptible to bulky waters such as Gyarados and Starmie.
I feel like Bronzong would be much more useful over Rotom as both a sunny-day user as well as a handy resistance for the team. It can definitely handle both Empoleon and Dragon Dance Kingdra (more common variant), and can also be EV'd to take a hit in the rain. Its bulk would be much appreciated on this type of team, and also removes your succeptibility to Tyranitar with Rotom. Scizor shouldn't be too much of a problem with Choice Scarf Heatran, and Gyarados can be stopped by Tangrowth.
Everything else looks pretty good, good luck.