Changing out the TVs is pretty simple, "IF" you can find a couple three ceiling joists to attach them to. In my opinion a 55" class is pretty big and heavy to attach to a motor home ceiling. Also the ceilings are often curved to match the exterior and they don't have an attic space so fishing an HDMI cable is going to be a chore.
We had a 1990 Bounder 27D and I ended up running the cable under the house and then thru the toe kick space under the kitchen cabinets and past the fridge and space heater. It was not easy and I wouldn't do it again. I only did it so when the DGKs were with us we could watch the same recording on both TVs. Now that they are older they don't go with us much anymore and with the Winnie and the living room slide we really don't use the bedroom TV, there is plenty of seating for four.
I would go wireless if I were to do it again. My time is worth the $300 cost of a full 1080 HD system.
I have no info on your current or proposed sound system but HES(home entertainment systems) are not cheap and the wiring is again a problem. The wireless transmitters are A/V so a sound bar and bass may be easier than a HES.
You don't have to buy equipment on ebay, but it is a go to place to see what is available. I bought all my stuff to sync my TVs and BluRay DVD player online at ebay. I don't think you'll be finding a 55" class set with a wall brick, so you'll be using an inverter unless you're in campgrounds all the time. All this stuff adds up and may require additional batteries if you dry camp.
Just some things to think about.
"I travel not to go anywhere, but to go. I travel for travel's sake. The great affair is to go". R. L. Stevenson
David Bishop
2002 Winnebago Adventurer 32V
2009 GMC Canyon
Roadmaster 5000
BrakeBuddy Classic II