As someone who loves sand so much, there are a couple things that would improve the team by a lot
First off, Skarmory > Ferrothorn. If you are using Excadrill over Garchomp as your main sand abuser, then Skarmory is almost a must have. Metal birbs in general are staples on sand teams because of their sheer defensive utility, being one of the few mons to hard counter Rillaboom. Of course, there are other options like Amoonguss and Tangrowth but by far, metal birbs are the best picks because they're immune to sand and they're also not that vulnerable to scale shot Garchomp, which is a mon that could give sand a lot of trouble. In this situation, Skarmory is better than Corviknight because Skarm can learn spikes and with rapid spin, you don't have to concede your own hazards when you need to remove the ones on your side of the field. Ferrothorn is not a good pick on sand because you are stacking weaknesses to Rillaboom. Yes, it stuffs banded Rilla but at the same time, can Ferrothorn actually kill Rilla? No and you lose to sd variants
Based on your team structure, the one thing that you absolutely lack is the ability to kill metal birbs. While metal birbs are great on sand teams, they are also the bane of sand teams. Neither Excadrill nor Garchomp can get past metal birbs and as such, one of your team slots must have the ability to get past metal birbs. Dragapult can somewhat get rid of them but it is not guaranteed. It is an option to replace hex with fire blast just so you can smack them. While I am not going to say it is required, but you might want to look at some options to fight get rid of them such as Magnezone or Dracozolt
A minor change, use specially defensive Hippowdon instead of physical. Your team is incredibly vulnerable to magma storm Heatran who can just pick apart your team one by one. Excadrill checks it but there is no way it is switching in to a magma storm
Here are the sets
Skarmory @ Leftovers
Ability: Sturdy
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Roost
- Spikes
- Body Press
- Iron Defense
Dracozolt @ Life Orb
Ability: Sand Rush
EVs: 148 Atk / 176 SpA / 184 Spe
Naughty Nature
- Fire Blast
- Bolt Beak
- Earthquake
- Draco Meteor
Hippowdon @ Leftovers / Smooth Rock
Ability: Sand Stream
EVs: 252 HP / 4 Atk / 252 SpD
Sassy Nature
- Toxic
- Slack Off
- Earthquake
- Stealth Rock
Note, if you want to use both Excadrill and Dracozolt, then you need smooth rock on Hippo. Unless you're really switching it in a lot, it can manage without lefties. If you want to use Dracozolt or Magnezone or any other answer to metal birbs, then it should be on the slot of Clefable. You could replace Dragapult but its speed control outside of sand might be too valuable to let go