Old-Biscuit's answer is the correct one. Sometimes they are call "salesmen switches" because the first thing the salesmen shows a customer is this switch when he enters the RV and turns it "on".
The switch is usually not for long term storage. It is for dry camping. It minimizes 12 volt consumption while you are out for the day. Propane detector and other vital 12 volt devices may continue to work.
Most salesmen switches do not disconnect 120 volt systems, but there is no reason why the switch couldn't do that. There is also not much of a reason to shut things off when on shore power. You can test it by plugging in and switching "off".
Do 12 volts still light up?
Do 120 volt appliances still work?
As you suggested there is most likely a relay some where that does the main switching.
Have someone switch it "off" and "on" while you poke around listening for the clunk of a large relay. There are new solid state systems that may be silent.
I wish you good luck and happy trails ahead!