Does anyone have a Oldsmobile delta 88 royal brougham that shakes the ground?

my 88 has an eclipse sw8200 12" sub (cannot be in ported box) hooked up to a JL audio 1800d mono amp.sounds thunderous inside. when i open the doors it can be heard a mile away. with the doors closed it cant be heard 15 feet away. is there too much flex in the trunk? will dynamat make it loud so it can be heard with the doors closed? what do I do. Need someone with competition experience to give me the solution. not "you'll go deaf" or some other wise azz comment. I am humbling myself before you more experienced audio folk. I know it would sound good in a different car