Depending on the condition, a strong marine compound if med/high oxidation, I have problems sometimes with heavy marine compounds drying on neglected boats, the gel-coat will just suck up most car products (have to work harder/use excess product $$). Once the oxi is removed and compounded,car products should be fine or if the boat is already in fair condition. I don't know every auto product out there, some do specify it can be used in gel-coat.