That rubbery stuff can trap moisture underneath, and if you ever get a fuel leak, say your stock Holley vac. secondary carb, the one with the fuel balance tube that uses O-rings which fail due to rot, and there is a spark from old wires, you've got a flaming ball of tar that can't be put out. Even dry Rustolium enamel will catch fire. I think the factory under coating was loaded with asbestos fiber, but it was limited to the wheel wells, you can check it out by seeing if it burns.,,, Safety first, which keeps me from wanting a fiberglass hood that can't be put out either.