Ya, what Sonnie said for placement
I don't think the walls will be the problem for vibrating your pj as much as the amount of bass you'll be pumping into the room. My subs are not connected to anything other than the concrete floor of my basement and the projector still gets a good shake during loud scenes.
Also, in the past I had a sub located at the rear of the room and it sounded great! Just depends on the room and the setup.
What drivers are you thinking of using?