I have a 7" G3X Touch Panel installed for the rear passenger. Configured as a second PFD - it should allow the person in the back to use the autopilot as well tuning the COM and XPDR. To attach the panel I have welded some distance blocks on the seatbelt attachment to have some "meat" for the threads. The seatbelts for the pilot are then attached normally. I have also a fully equipped rear stick and a flap switch on the backseat panel. The grounds for those functions are over a switch in the front so I can disconnect the functions of the rear stick and flap switch .
I am using GRT for the front for my second RV. GRT is a fantastic company. for the backseat ILevil AW with an IPad. The ILevil has a WAAS GPS and flight instruments will supply several other units via WIFI.