Rust stop/proof inside an inaccessible area?

[Condi]

Can anyone suggest a spray in/on rust proofing which can be sprayed into a void? I have rust stop chemical which is applied by brush but will be unable to access with a paint brush. Hammerite do paint cans which you can spray on rust, although it seems to just cover the rust rather than chemically stop it. The void has had water in, and hence is rusting from the inside out. I can stop the water getting in, but need to stop the rust spreading.

[Andeh13]

Behind radiator paint brush?

Buy lots & slosh it in?

Compressed air, a pipe & expect some of mess?

[InitialDave]

Rustbuster (www.rust.co.uk) are probably the people to talk to.

Though if water is getting in and not out, tactically placed drain holes would be my first step.

In terms of application, I've used Machine Mart's cheap shutz gun with its included extension probe to good effect.

[Fastdruid]

Dinitrol RC900.

It's an aerosol/spray can. You can get other nozzles for it to direct it more into closed cavities etc.

Dinitrol also do rust proofing cavity wax, I think it's called Dinitrol ML, again an aerosol.