I can't help you with the install but I can tell you this... I have owned a 2006 Sea Breeze.
Im guessing that "cab tv" is the one in the front over the drivers and passengers seat?
If I understand you correctly....
I think you are talking about mounting a 39 inch tv, on an extendable mount, and installing the mount in the back of the existing cabinet area where the old tube tv used to sit, with the tv mount extended out.
I feel this is a really bad idea, and others might chime in and agree!
The new 39" tv on a mount, extended out, bouncing down the road could be a huge disaster!
In a worst case situation... the tv mount stressed from being extended rips off the wall, the tv falls on you, the dash, the steering wheel, your wife, a pet, causing damage to the coach...possibly causing you to have accident, or worse.
From what Ive seen, the way the professionals seem to do it is they create a new front panel that attaches in its place like where a cabinet door would be. It is then extremely securely mounted to the cabinetry around it to hold up to the constant weight and vibration. Then they take the new tv and mount it using a flush style mount to this new front panel. Lastly drilling a 1-2 inch hole in the newly created panel to feed the wires thru.
If you have room and in certain situations, professionals can make the tv on a swinging door giving you added storage space behind the newly installed flat screen, where the tube tv used to sit.
The picture below is one in my coaches bedroom and it is mounted on a swinging panel
as I am describing.
If I am wrong on any of my assumptions above, I apologize in advance. Just trying to help.
Good luck, be safe and if your not sure.... pay a professional.
2019 Fleetwood Southwind 37 F
2018 Jeep Wrangler JL - towing
2020 Jeep Gladiator Rubicon - not towing
We RV'd ALL of the lower 48 states and into Canada