Uh huh…
Deadening and amplification and/or new door speakers are the correct way to go. How does stashing electronics under seats where they can overheat and get damaged even sound like a remotely good idea to anyone? Not to mention there isn’t any airspace, nor enough depth, to properly achieve ANY subbass.
And bass shakers weren’t speakers as much as they were vibration devices similar to whats in your cell phone. for-effect devices only.