Before I started at my current work the guys went around and put what’s called Navy Steel rust converter on rusty pipework to slow the rust and allow time to plan and carry out proper fabric maintenance. (Offshore apparently have used it as well.) This was done at a gas terminal which is on the English coast. I assume the loose rust was removed with a wire brush/scraper and then the converter applied. They sell to other folk and maybe it’s what rust buster sell also. I’m a skeptic to rust converters but must admit it seems to have worked and haven’t noticed any of the covered areas getting worse. Could be a good item to inject into car cavities before the rust treatment and maybe a good temporary rust barrier for items waiting to be painted etc. Their website is but not sure if they sell to the public. https://www.navysteel-rust-converter.co.uk/ I have nothing to do with this company, just in case folk are wondering.