Linear actuator arm would require an interveing arm that would magnify the limited piston travel into a more lengthy movement in order to move the item through a full 90 degree swing. A somewhat trigometric problem as you can see. The roof probably has one rib member from which you could safely hang the TV weight; but you need an additional framing member for the actuator to attach. A surface-mounted backing apparatus would have to span 2 roof framing members. Not a DIY job that I would encourage.
I would look to custom coach or cabinet shops that have done this in the past [if you are dead set on a automated fold-down] You are not the first to want a disappearing screen.
Apart from the wow factor, would a simple hinged-and-gravity-fall arrangement do just as well? You could conceal the tv via a mirror-faced wood/fabric frame. A hidden release latch & swing-it-down to vertical? Power & HDMI wire could be run via A/c ductwork in the ceiling & fished-over to center via the polystyrene foam barrier. Are we talking 37" size?
2004 Tiffin 34XB,Workhorse.22K,8.1L,Gas