I'd go with Magnemite and Swinub.
Magnemite, because having a Steel type on you comes in handy and Magnemite isn't of the stupidly slow Steel types. It can also learn:
Discharge - REALLY good in doubles, especially on a Factory/Short-Circuit field.
Flash Cannon - Just a strong, special Steel attack which gets a boost from the fields mentioned above.
Tri-Attack - A good alternative to Thunder Wave, since it's powerful and can inflict 1/3 status effects.
Hidden Power/Electric Terrain - Hidden Power, because there's no telling what type it'll be. As long as it's not Electric or Steel, it's fine. Alternatively, Electric Terrain is good for those Gym battles where the Field is hindering your Team's ability to strike effectively.
Swinub because you don't have any Ground/Rock/Ice attacks to combat Fire/Flying/Poison/Dragon types.
Ice Fang/Icicle Crash
Earthquake
Iron Head
Body Slam (Ancient Power so Piloswine can evolve into Mamoswine)