if you're gonna go the prep paste route,mask the panel gaps with 3/4" tape(picture outlining where they meet with tape)that way the sludge doesn't run into the jambs.that stuff gets into everything and follows every seam/body line/crevice etc.when you're all done pull the tape and dry scuff those small areas by hand that were previously masked.you really need to stay on top of that stuff if you're using it on a car vs a single panel on a stand.it gets a little messy and making sure you get all of it off is important as when it dries it becomes another contimant in your finish