What kind of rust preventative you need will probably depend upon the humidity in which you live, and how the gun is stored.
I live in the remote Utah desert. Humidity can be high at times, but on the whole it's low.
So, I use olive oil to protect my black powder arms. It's all that's needed.
My guns are stored in a gun safe, in the house, away from moisture-attracting dirt and dust, and extreme temperature swings.
And I never store my guns in a case, box or plastic bag. Air circulates inside the safe, keeping moisture from being trapped.
A glass of ice water soon acquires droplets on the exterior of the glass, through condensation.
Same thing can happen to a gun left in a cold vehicle, then brought into a warm house: tiny droplets of moisture condense on the surface, promoting rust.
For me, olive oil works fine. If your guns are exposed to humidity or temperature swings, you may need something more protective. But I think you'll find that olive oil, and checking the gun for rust every other week or month (depending on rust-promoting conditions) will keep it rust-free.
"And lo, did I see an ugly cat. Smoke. Brimstone. Holes in parchment. And this ugly cat was much amused." --- The Prophesies of Gatodamus (1503 - 1566)