I can't help with Stockpile. I am also not a "pro," but I can offer you what I run on mine. Other people will have better suggestions.

Nature: Careful, 188HP/176 SpD/144 Def

Ability: Thick Fat

Item: Many things can be used here. Leftovers would make sense with this set, but I run a Bold support Whimsicott with this Snorlax who has leftovers so I have to use a different item. Chesto Berry works well also.

Moves:

Curse

Rest

Giga Impact (Return would work well and probably better, but my Snorlax is not max friendship)

Crunch to deal with Ghosts or you can give him something else if you have someone else in your party for that.

I have used this set extensively in Battle Maison and in some Wifi battles and it hasn't failed me yet. I run it with support Whimsicott that knows Moonblast to cover fighting types. My Whimsicott runs Stun Spore, Moonblast, Leech Seed, and Encore with Prankster as the ability.

I will usually start the fight off with 2-3 Curses. With Whimsicott, I will immediately remove any fighting types to eliminate Snorlax's biggest threat. If an enemy is present that can OHKO Whimsicott, I will usually be forced to switch out. If it's a neutral threat, I will start setting up leech seed or go for Stun Spore if I see any potential taunt users. Once Whimsicott has double leech seed + leftovers set-up, it is pretty hard to take out by anything other than a strong STAB fire or ice move. If an opponent tries to set up on me, I will use Encore.

After 2-3 Curses, Snorlax will more than likely have taken some damage, in my experience about 50%, and then I will use Rest. Once Snorlax wakes up, he's pretty hard to take out and +3 STAB Giga Impact seems to one shot just about anyone. Return would do so as well I imagine, but I have raise his friendship.

This opening set is EASILY countered by a Taunt user or a pokemon like Blaziken, who can heavily damage both Whimsitcott and Snorlax.