[kyleb]

"Now for the problem : the threaded inserts for mounting are in the plastic case of the TV . This allows a lot of flex which wouldn't be an issue in a static environment , but I think the case will crack in highway use . "




Thanks for that - Now, I have to worry about dadgum thing hitting me in the head while riding down the road !    

I was thinking that it's just my Vizio that has a "flexy" mount , but closer inspection reveals that your's is also a Vizio.
On mine the mounts are on 100 mm spacing and are captive nuts in the plastic case which is about 2 mm thick . Your mounting bracket looks very well made , just wondering if you have a provision that steadies the TV . My time is limited , was hoping to go with store bought , but I think I will have to fab something similar to your's or use a horizontal slider .
All the help is very much appreciated !
Thanks ,
Chris

I made mine out of 11 ga carbon steel. The mount is not rigid where the tv mounts, so it shares some of the flexing.
I don't notice mine flexing while going down the road.