dieharder wrote:
So something like this should work?
That will work to physically connect the things together, if I'm understanding what you have properly. Whether or not you'd get sound out of the speakers depends on where the other end of the cable with the headphone plug goes.
If it goes to a radio or other unit with an amplifier, then you should be good to go.
If it is directly connected to the speakers, then you'll need some amplifier to drive the speakers; the new TV's RCA output won't do that. Something like
this little unit would probably work nicely and could be directly powered your 12V power system and not break the bank. (The output ratings of this, and unfortunately many, cheap amplifiers are wildly optimistic. It still should work OK for this use.)
Before buying anything, I would probably see if the speakers built into the new TV are adequate for your needs. If so, using them is the simplest and cheapest route of all.