3rd Gen Onix?

So here's the scenario:

I'm doing a Dragonesque Challenge in my Pokemon Fire Red. Basically, its a Mono-Dragon Challenge with Kanto Pokemon that can pass as Dragons (be it by their typing, influences/origins, or use as such in a Dragon Trainer's team) because the Dratini line is Kanto's only proper Dragon Types.

My team so far is Lance's team (Charizard, Gyarados, Aerodactyl (still Old Amber at this point), Dragonite (still a Dratini).

I also have Onix (who is partially based off of a Wurm, which is a type of dragon), and I plan to add Lapras (as it is in Iris's Champion team in W2/B2).

The thing is though, Onix is almost completely useless. He has an Impish nature and his stats in general (bar physical defence) are mediocre at best. Maybe I can make up for his lack of good stats by giving him a good moveset and that is why I need your help.

Can/Will someone give me a good moveset that I can teach my Onix?

If Onix is ultimately not worth it, I'm considering replacing him with Rhydon (my justification for which is that Iris uses an Aggron and Rhydon is essentially the Kanto equivalent of that Pokemon).

What should I do?

I don't think Onix is really worth it unless you evolve it into Steelix. Earthquake and Iron Tail are pretty good moves on him. You can also run Toxic if you need to stall out someone throughout the game. Using Rhydon/Aggron would open up more doors for movesets. It might be worth making the swap.

I think you should just use Rhydon. Onix is really only useful if you evolve it into Steelix.

As the others said, try using Rhydon, because unless you evolve an onix, it's absolutely completely worthless. The last time I tried using one was in Gold. Nicknamed Rocky, it was the same one you get in Violet City for a bellsprout. Raised it to fifties, and did it keep disappointing me! In the beginning, it felt super awesome; the amount of damage headbutt and rock throws did to ratatas, but as I kept going.. *sigh*
So yeah, since you get a Metal Coat on Island three (?), which is pretty late in the game, I do not recommend using that dick pokemon ;-)