Peel-n-Seal with foil tape on the seams, is my choice. I have used it on several vehicles, some approaching 10 years, in service. The factory sound deadener used on the floor of the '60-'66 Chevy/GMC trucks has been in place for 45+ years. When removing it, I have never found any rust under it. In fact, the paint looks brand new, if I am able to peel back a sizeable piece, otherwise, I use a wide blade chisel in my air hammer, to carefully remove it, without damaging the sheetmetal. It is asphalt impregnated, as many of the sound mats.
