Question (then answer) do you want to watch the SAME SHOW on all TV's or do you want to watch different shows in different rooms?
Answer. Do not access the rear of the TV (though it may be way easier than you think) Access the switch box.. Somewhere in your RV is either a wall plate or a box of many buttons.. I gather this is where you can get to it easily to switch from OVER THE AIR, to Park Cable.
All the connections you need are here.
If box of many buttons they are labled on the back you will need a coax jumper or two, and possible a "Joiner" (Double female, or barrel connector)
Pull box, find lead to MAIN TV, disconnect it and connect to decoder box. (TV-OUT) hook jumper from now vacant port (MAIN TV) on switch box to decoder
If the other TV is equally hard to get at you can do the same thing with it's lead here.
On the wall plate,, if you have one,, Usually the main TV comes off the front, But if not it will be the 3rd (or 4th) connector on the back,, Viewed from the rear with the 12 volt accessory socket at the top.. The cable are, In order
1 (left most) ANT
2: Park cable in
3: TV-2 out
4: (Optional) Tv-3 out
You can make the same type of change there.
IF you are only going to watch same show on all sets
Disconnect park cable from Switch box.. Feed to cable in on decoder, extend if needed with jumper and barrel connector.
Jumper from TV-out to the now vacant Park Cable port on switch box.
Trust me, (I just did a mod not much different than that) Easier to do than to type.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times