I have an idea for mounting a larger television on a drop down mount with a slide but I will need good ceiling support for mounting(thinking rivnuts and machine screws) but I need to locate the ribbing, without removing the headliner. Any ideas?

rivets on roof line up on framing.

I am interested how your install works. I have read flat screens do not like riding on there backs. That may be for older back lit units not led back lit screens. I think they are lighter.

The roof frame ribs are a square aluminum tubr so unless you go all the way through the roof I don't see how you would get a nut on the machine screw. The alternative would be very stout rivets. To find them have you tried the knuckle stud detector? Tapping with your knuckle may give you a good idea where they are just by difference in sound. As was said before, the rivet pattern on the roof will tell you where they are, but if you have a coating up there they may be covered up.

My Regal has 2 small screen may be 12 inch TV's one mounted in the front between the overhead compartments and one in the bedroom. Will be very curious how you work out the revision. Hope we get PB to work again...

I am an IT guy and a 25 year electronics tech and thought I would respond to LCDs on there back. This especial applies to larger screens. The way an LCD tv is constructed is the weight of the screen is balanced for an upright position. If stored flat the screen can distort or crack. The larger the LCD the worse the problem would be. Kind of like a piece of 1/8 plywood. That being said, small LCDs hold up better on there backs because there is not as much weight from the LCD.

I understood that the roof frame is framed every 12" on center 1" aluminum tubing. When I walk on the roof I try to stay on the frame vs inside the frame. Any seams on ceiling should be on a frame rail or the cabinets may be screwed into a frame rail. Do you have any blueprints? Rivnuts with weight of tv could work, may work their way loose over time. Depending on whether you decide to fold up tvafter the post from Paul & Jaime.
Tere