I'm hooking a carpc to my campervan. I know it's not the same, but I'm planning on using a laptop and a touchscreen in the front. I don't know how large your rv is, but for me space is premium.
The other reasons I wanted a touchscreen up front was to give me GPS and a rear view camera for parking. The laptop will be removeable since I hardly ever use my van.
There are plenty of dual-monitor graphics cards out there, I used to have a Matrox g400 and it was great. See if you can find one on ebay or something. It had two vga outs, and you could clone or have an extended desktop. The second VGA also had a VGA-RCA/S-Video adapter in case you wanted to use a television.
Why do you need two sound outputs? It seems too redundant to have two sets of speakers in the vehicle.