If you can get a coating around rust that stops the air it will stop or at least slow it down.
If you used the Innerpanel Rustproofing stuff from Rusfre , kerosene is used to thin it down.to help it go threw the gun. Thats the way it used to be. And kerosene is a little like penetrating oil,It will creep into and soaks into the rust some. But I am not sure if the EPA or anyone has changed the way you use it. Been awhile ,and the Innerpanel Rustproofing stuff is the only one I use ,It stays soft and the rest of the stuff will get hard and crack, but I make my own out of ''boiled linseed oil'' A small bottle of STP.
https://www.google.com/search?q=stp...u&sa=X&ei=je7qT4OOGKqA6QGi67DiBQ&ved=0CGIQrQQ
And some times paraffin wax But with the wax you need something hot to melt it all together without it exploding .
1....Get some 'boiled linseed oil'' about a gallon at Lowes
2... a bottle of STP to keep it from getting hard , and help it cling .
3... A gallon of white kerosene to thin and help creep.and the rest of the kerosene is for clean up. not sure of the mixture , just thin till it will spray good and creep well.I spray a thinned down coat first''saturate'' and then a little thicker for the second coat.And yes it is a dripping mess.
Worked at a Subaru Dealer when I was a kid , and that is what we used . worked great and was cheap at the time.
Not a good thing to spray on outside of the frame , makes a mess, Drips for days.I had a Toyota pickup and would not stop rusting big flakes off the frame . finally sprayed that on the hole frame, inside an out. drove it for a week till a dirty dry coating formed on the top and sprayed some cheap enamel black paint over it . finally stopped rusting...
If you try the boiled linseed oil ,Do it somewhere you can make a mess and let it drip for a day or even a week
But the Rusfre inner panel product is good if you thin it some.
if anyone uses the gun to spray , keep the air up enough to blow the undercoating out hard to force it into all the little corners .''saturate'' key word.
'boiled linseed oil'' is old school But still is a great product it was used on the farm for all your tools when storing them over winter to stop them from rusting .