Forget the trunk paint, it washes off with water! In fact, forget about coating it at all ... the last thing you need is paint chips or dissolved paint on your parts. Let the grease and oil from your parts be the treatment. You might also consider a piece of sheetmetal for the top or even a couple of dollar store rubber boot mats - they're ok with oil and solvents and have a nice ridge around them to keep liquids and parts from ending up on the floor (as well as protecting the bench top).