why not somenoe from Mamoswine line then? its immune to both SS and Hail. Also, for item, i would go lefties, and would give it protect too. The reason is simple: with protect, 2 turns of lefties = damage from SR neglected, bringing you back to full HP. For last move you could go a trapping move or worry seed, to f*** those Magic guarders on the switch 8D
So, IMO, the best set would be:
Swinub/Piloswine/Mamoswine level 1 @ Leftovers
Trait: Sturdy
Whatever nature and EVs
-Leech Seed
-Toxic
-Protect
-Worry Seed/Wrap/Whirlpool/Gastro Acid
EDIT: I wouldnt go Attacking-Trap move. Non-Scarf blissey could kill you otherwise, with leech seed + damaging move. A good option would be Spikes, for support or endeavor (but that would mean you are NOT brought back to 100%, meaning endeavor is a worse option.
Conclusion: Worry Seed, Gastro Acid or Spikes ftw