use tape and newspaper to mask off the area you want covered. get some black rockerguard or rubberized undercoating, either or. aresols avaliable at the parts store. scuff the area with a kitchen scotchbrite and wipe clean. spray on and use light coats, letting each dry a bit or itll run. rust wont eat through for a while, and when it does, squirt, done.
this tip also works well to hide duct tape repairs. good for inspection around here.
94 V8 on 17" custom paint, R.I.P
97 Mark VIII LSC yeah
08 Ford Edge, white for now