In my region, Vermont, (NE USA), rust is a real killer as we have damp climate which is at the killer temperatures from 32 to 45 degrees F. much of the year. I am patching rust below rear windows and hatch as well as floorbds. and sill and bottom of doors. So far not too bad.... but one more year this car would have been a 'goner'. (our inspections don't allow holes into passenger comparment... besides a real danger to occupants from exhaust gas.) Many old timers in the region spray old "hot" crankcase oil into body cavities. It's a very messy job. So far I am only using triple doses of "rust converter" coatings (one every two minutes 3 times.. then finish with rust preventative paint the next day.) Then I am spraying underneigh floorbds and wheelwells with rubberized undercoating (10 to 15 bucks a can) and then into cavities of interior body: 3M's panel rust protective coating (a clear oily finish) about $15 a can).....

I am thinking of trying the 'famous' POR 15 next spring after I see what rust 'blooms' after my initial rust hole filling this fall.

I am interested in trying the oil coatings, but not with any risk of staining inside carpets. .......