I'm sure if you poke around on all sides, there is something holding the TV down. No easy way to tell how they did it without getting into your RV.
Never heard of mounting the solar panel to the AC unit. The cover would not be strong enough, so you would have to build some sort of frame that would attach to the bolts holding the AC unit in place but you would need to do it without compromising the seal. Then you would have to consider the sail effect. Being up away from the roof, if wind can get under it, doing 70mph into a 30mph headwind (say downhill on a grade), it could create a lot of lifting force.
Yes, there are ceiling joists and obviously, you would want to bolt into those (and seal the holes well). You do want spacers so air can get under as solar panels don't like to overheat (tyically an inch or two). Of course it needs to be sturdy as the sail effect can still happen but an inch off the roof will typically allow less of that effect than a foot and a half above the roof.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV