How do I protect chrome before there is any rust, and right after I have removed rust off of it?

Chrome does not rust, its the steel under the chrome that rusts and flakes off the chrome. In the UK the number one product for chrome is Solvol Autosol. Does what is says on the tube.

Once you have removed rust, use vaseline (yep it's weird but it works :p) every now and then to protect the chrome parts.

When you notice the parts starting to get opaque use light abrasive paste on a cloth to make the chrome parts shining again.

I got most of the rust off then painted the chrome with wax oil

What ive done is get a mixture of engine oil, new oil mind you, and diesel. Now get a suitable amount in a container, that your sure of will cover the entire chrome base youre looking to protect. Once youve got the mixture ready, pressure spray it onto the desired areas. It will attract dust and dirt. It will. But no water can destroy it. Or if you want extreme protection use only engine oil. Similarly, it will attract dust and grime. But whenever you clean it, it will shine like a mirror! Thats what i use to keep my chrome rims from getting anything on them.

Don't use anything based on petroleum. Petroleum based chemicals turn acidic over time. Use this method to protect your chrome: 1) Polish with a good chrome polish. 2) Apply a top coat sealant or synthetic was. (video here)

Chrome plating has micro cracks in it. The copper and nickel plating under the chrome do most of the corrosion protection of the underlying steel If rust has shown on the surface, the copper and nickel have failed at tiny locations . A low viscosity oil will penetrate the cracks in the chrome and give some protection to the steel . Not many other choices. I have dissolved grease in gasoline and wiped it on the chrome . My plan is the gasoline carries the grease through the cracks and then evaporates leaving grease on the steel. I don't know about chrome on zinc die cast , but oil couldn't hurt.