I have the scangaugeII in my rig as well - This is the location I found works best for me:
As you can see in the photo, I used small adhesive clips to manage the cord. Using these clips and velcro on the display, I can easily move the gauge from the RV to another vehicle.
Ignore the wire running diagonally - it's another one for my handheld GPS.
The plugin & iPad display sounds interesting as well. I can see where that would be very useful when trying to troubleshoot an issue, but for day to day use, you'd need to dedicate a device to the application.