Since we are leaving Sunday with 2 of the grandsons for Kansas City, I installed my initial effort at a more permanent solution in our wagon.
BJs Club has an RCA full 1080i 24" TV with DVD player on sale for only $149, and the only one in stock had a heavily damaged box so the manager gave it to me for $129.
Since this was way less $$ than the other solutions I've beeen exploring, I figured I'd give it a try for this trip and go from there. In trying to decide how to rig it up temporarily for the trip, I remembered I had an extra mount lying around so I used it.
I screwed a 1x4 into the pillar behind the plastic trim, then screwed the mount through the wood and into the pillar. To stabilize the assembly, I ran a 15" old school rubber bungee from the arm end to the headrest.
I mounted it lower than I might have so the boys don't have to stare up to view it so much, and high enough to view okay from the rear rows.
I tested it out on a quick trip out to Disney yesterday (only 25 mins from the property) over bumpy back roads with wifey's erratic driving, and I couldn't ask for a more stable picture. Sound level is fine for now with the 3w simulated surround speakers, though I'm looking to get a headphone IR receiver to add, and there is digital coax audio out should I want to add surround sound like we had in our last van...
It has inputs for HDMI and VGA as well as component and (crappy) RCA video, and a USB port. Also, I like that this one can be controlled without the remote which many new TVs don't have now.
I'll let you know in a week how it worked for the road trip!