to undercoat or not to undercoat???

Definately would apply something between your car and the elements.Worked at a rustproofing business for a few years(7) in Canada and was the quality control inspector for S.E. Ontario for one company.Good thing is you have a very clean surface to start with.It takes about the thickness of a playing card to properly cover an area.Make sure the area you are doing is totally dry so you don't trap any moisture as it will bubble and be prone to peeling.Also check and touchup any areas that might need to be done before you do any summer cruisin.GL