CLR is great. It removes rust stains and oxidation from paint as well as some of the rust. My '53 was really bad so I spent some time scrubbing down the worst rusty spots with a green Brillo pad and lots of water. I then washed the whole thing with CLR.
I live in southern Iowa- right in the rust-belt. 10 and 15 year old trucks around here have rust holes you can stick your hand through, so slowing or stopping the rust was important to me. I didn't want to clear-coat it because that looks unnatural- kind of plastic- and it really darkens the rust. Car wax works OK on good paint but can be hazy on old paint and turns white on rust and scratches. My solution was to use furniture paste wax. You can adjust the level of shine, it's invisible on rust and rubber, and it's more water repellent than car wax.
If you look in the upper right hand corner of my photo you'll see rust free bare metal. It's been that way for about nine years now with no signs of rust.
Is there really any thing you have to do to preserve the look. After all its been achieving that look naturally after many years....just let it continue if rust through is not evident.