I have a Pi 2b Set up in van, with iPassPort keyboard (here)
Run it off a usb mini power converter similar to this. Usb power plug is almost rooted.
Powered from 12V accessories.
I have a 2TB toshiba 2.5 in portable drive plugged in that on the odd occasions shows the rainbow box in top right corner on boot up.
Also a TP-Link usb wifi (TL-WN725N 150Mbps Wireless N Nano USB Adapter) to allow van to connect to home wireless for updates etc.
Standard Video out (not HDMI) connected to RCA inputs in car (correct cable requried, check here)
Did play with UPS Pico for a while, very technical, got it working, albeit, couldnt get the voltage drop sorted due to External USB HDD (Check here for details)
UPS Pico eventually had a fit, and am waiting for the new version from Europe.
All that said, most times we remember to stop the movie (X Key), and sometimes I bother to shutdown.
Lots of times I have shutdown with movie paused, or even playing.
Had this running since about July 2015 (at time of writing this, over 1.5 years.)
Only had one file corruption, but was easy to diagnose and replace.
Note: We are in Australia 
Hope this info helps
Junkie