Need help on Attaching Screws in TV BOX ceiling

I have never seen an RV with less than a 2" thick roof. As long as you keep your screws shorter than that you should have no problem. Finding the actual roof frame itself might require a little trial and error or tapping with a hammer to find the most solid portion of the roof. Look for existing screws that already attach your upper cabinet to the ceiling.
Some coaches, like mine only have an aluminum roof frame so I need sheet metal screws to attach anything.

I don't think you will find wood in the roof of a Newmar. They have aluminum frame construction.

The roof in a Newmar, your year, is about 6 inches thick. BUT, you are trying to install a mount in the front center above the dash where the CRT TV was? If so, there is a aluminum and a steel cross member in that area. Yes, the crossmembers in a Newmar are aluminum. That whole overhead dash cabinet is not just mounted to the aluminum substructure, there is that steel cross member. It will be hidden by the ceiling fabric material. You may have to try to poke holes thru the ceiling panel INSIDE above where the original TV was to find the solid cross members. That is not a bad thing since your new TV mount will cover the holes. What we do is make and install a 5/8 plywood plate on that ceiling with the gray storage type floor material around it and hit those studs and then mount the TV to that plywood plate. Doug

My Ventana has a layer of plywood behind the ceiling vinyl. the roof is about 4" dp. Trusses are aluminum. The plywood was more than adequate for me to screw into, I would imagine your Dutch Star is similar construction. I built a completely new equipment cabinet and had no problems attaching it to the ceiling