Thanks to everyone who offered suggestions on how to remove the old TV. I am finally back home and ready to proceed with the renovations. First, to answer a few questions, the original cabinet did in fact have doors which were removed at some point leaving the cutouts for the hinges on each side. If there was ever a slideout in the bottom of the cabinet it was most likely removed to install a larger TV. There were three or four screws on the interior of the face frame that I originally thought held the trim in place but even after removing the screws everything is firmly attached. Possibly they screwed and glued the faceplate back on during the previous changes. I have looked under the RV and see nothing to indicate that the TV or cabinet is attached in any way through the floor. My next step is to try to carefully remove the top of the TV cabinet so that I can see the inner workings of the cabinet. The opening will not be big enough to remove the TV but at least I can get a few more ideas on how to proceed from there.
With regards to the cables I was able to find an old wiring diagram in my manuals which indicated there was originally a splitter mounted somewhere between the VCR and the three TV outlets. Obviously this was also changed along the way with no sign of the new location of the splitter. The old antenna has been replaced and a new coax runs directly to the selector box providing a good clear signal to both inside TV's. The original booster for the antenna did not work and in fact apparently never worked for two reasons. First, there was never a ground wire installed to the switch. I had 12v power but without the ground the signal was not being amplified. Second, due to the splitter which was apparently between the booster and the antenna the amplifier could not do its job. Bypassing the old cables (which I removed by the way) and installing a new cable has resolved this problem.
My next step in this process will be to install a TV in the cargo bay and see if I can get a clear signal either from the OTA antenna or the satellite through the selector box. Following that will be replacement of the old VCR with a DVD player once I am able to access the old TV in the front and gain access to the A/V cables.