I have the PC-104 stack built with the Vortex86DX core for the brain of the Mantis. I have added an 8 port RS485 transceiver board with baud rates of up to 921.6Kbps, I don't need all eight ports, at least no yet, but it was the only board I could find that had the high baud rate capabilities, at a reasonable cost. The Vortex board will only go to 460.8Kbaud.
Installation of the serial baord in Linux was a little fiddly, but thats brobably due to my lack of Linux knowledge. Currently I only have a single port running on the 8 port board, well actually I can have any of the eight ports, but only one at a time. So that's good enough for now!
At the bottom of the stack is a PC-104 PSU, that takes 12 to 30V and delivers 5V to the stack.
I have placed the stack in an old CanTainer I had, but I will purchase a new CanTainer for the final unit, and machine the case tops with the appropriate connectors.