Zinc galvanized pressure pack you can buy this in a spray pack and then paint colour over the top of it. uses a wire brush back the affected part or spray on the bit that you really wanna protect i don't know about the bike that i spray my wheelbarrows in other things are outside with it
we paint absolutely everything we could use in steel with it over here on the beach
if it is a really rusty first use a well priced rust converter would you can buy this turns rust black and stops the process and treat with zinc galvanize
P enetrene its best for loosening rusted components

Boeshield T-9? is the go and you can get it at some bike shops. Not cheap but it not only protects from rust but also lubricants. I use this on my ebikes as I use cr mo frames and through all the rain and muck it does a great job. Good for the chain as well.

How about a natural pond from Bonominator