How to scuff and paint metal inside cowl?

The Eastwood stuff sounds interesting. Has anybody here used it?
What I've always done in the past is get in there with whatever I can- steel wool, small wire brushes, etc. and get it as clean as I can.
Then I hit it with a can of rust convertor, and like @1WildRT said; replace the nozzle with one that lets you stick a straw into the tip. And then soak the living snot out of every surface and crevice you can reach, through the vent holes and through the cowl slits. Then after it dries, hit it the same way with a coat of paint, as best you can.