I would say..
Blastoise (M) @ Leftovers
Trait: Rain Dish
EVs: 160 HP / 96 SAtk / 252 SDef
Calm Nature (+SDef, -Atk)
- Surf
- Ice Beam
- Toxic
- Iron Defense
Now for the moveset, I like it, but you could try this.
Blastoise (M) @ Leftovers
Trait: Rain Dish
EVs: 252 HP / 136 Def / 120 SAtk
Calm Nature (+SDef, -Atk)
- Surf
- Ice Beam
- Toxic or Protect
- Aqua Ring
This is just pretty much having so much Hp restoration its not funny, although I would go with your set, this is always an alternative.
Hope I Helped :D