Adding my last layer of undercoat tonight as a matter of fact. Putting in over the just painted chassis coat black floor pan repair. Messy, and let it be years before I have do that repair again.

Get some Duralast or Good Year spray on undercoating and sound deadening down at the local auto parts store. Take a stiff wire brush and and knock off the dust and residue. Also use a good strong degreaser, rinse and let it dry well before you apply the undercoat. If you find a rusted area I highly recommend getting a can of Por 15 and a can of the Chassis Coat Black. If you order POR 15, the Marine Clean is a very good safe degreaser they sell. The POR products are well reviewed here on the BB.

Follow the directions on the Por 15 and Chassis Coat paint to fix any bare or rusted areas.

Spray on the undercoating to add another layer of protection and fill any spots were the old coating is getting thin. It is not expensive, lasts and can be reapplied as needed. Unless you like that fresh tar look, gloves, safety goggles, and sleeve up when you apply.

Regards,

Paul