I have a friend doing the same on his banging his head, rig same as yours. Your cabinets are screw together with wood strips holding cabinets to walls and other cabs. If you are lucky you might only have to remove TV cabinet in chain of cabs, remove and cut back side of cab and than remount. When you measure for TV make sure you have space on left hand side to mount LCD most come with spks on each side for stereo sound. You may find one with spks on bottom and a built in DVD player.
For mounting you could go to my post in Newmar Forum to give you some ideas, the space in box could be built with shelfs for your DVD's.
Have fun and good luck with your project.
Would say your headliner should go to windshield.