I used a product bought at FLAPS called Right Stuff. One quart about 5 bucks. Has phosphoric acid. I put in a spray bottle and pumped into frame nooks and crannies. Smells a little nasty and turns black when dry. Seems to work OK. I them cover with a primer. Directions say to use above 38 degrees but I've used at lower temps just took longer to dry.
Dan
