Well, first off I'd recommend not using Mud Shot at all and grabbing the TM for Bulldoze instead (South Boulevard Pokemon Center in Lumiose for 10,000 pokemonies). It's an all-around better move - more power, more PP, higher accuracy, same side effect, plus it's a physical attack, which is better for Chesnaught in the first place.
Anyway, I'd replace Rollout. Bulldoze still gives you coverage of Fire- and Ice-types, and it gives you coverage of Electric-types as well, which of course no other type does (while you can use other Pokemon to cover Bug- and Flying-types). Actually, I'd probably replace Bite as well, with Shadow Claw, which is more powerful and gives you the same super-effective coverage. The TM is in Glittering Cave, according to Bulbapedia.