They make just about everything else for RVs (including special-sized toilet paper!), it seems to me that someone would have thought of this, and maybe they have:
Specially designed intercom systems for RVing.
We have a itty-bitty Gemini (Class C), and my wife sits on the bench behind me when we're on the road, and she cannot hear me unless I yell, and vice-versa. I cannot imagine what it must be like in a Class A Land Yacht.
So...is there a solution out there? Someone MUST have thought of this! (And yes, we've tried walkie talkies, but what a pain in the butt, you gotta remember to charge them, they sound like crap, and you're actually broadcasting to the immediate surroundings.)