WIthout a LONG RCA cable (Female to male) running the length of the camper, I don't see a good way of doing this. (Though that will work!)
I also gave this some thought and I decided a small footprint 30 dollar DVD player and a 15 inch LED TV (bought for 100 bucks) at a electronics box store was the hands down easiest and cheapest solution.
You don't need surround sound in the bedroom and the stereo already plays there on speaker C anyway.
When boon docking I normally don't bother hooking up the bedroom TV at all. It does pull much less power than the bigger one in the living room, but who wants to watch TV on a 15 inch when the big one is available?
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW