Im replacing my 4in straight pipe on my LBZ Duramax with a smoke stack. I’m leaving the 4 in from down pipe to my new 5in stack. My real question is, how big should I make the hole in the bed for the stack? The stack is 5in Inlet to 8in outlet. So I’m wondering if, instead of making a 5 in hole in the bed, should I make one slightly bigger than 5in? And do I’m wondering if I need to fabricate some sort of 5in rubber seal to go between the stack and the hole in the bed, to eliminate vibration from the stack. I’m assuming the stack would rattle and vibrate the metal bed. Help!