Same here... i just stopped making trips unless absolutely essential because i couldn't cope, i would end up crying too because there was nothing i could do.

I would say your best bet is to sit in the back with him so he can see your face and hold his hand...

In our case in hinesight i know it wasn't so much the car or the seat but that it was a period of time where he wasn't held by me and not being able to see me made it worse. Things only got relieved when we turned his seat around, and even now he is not good on car trips over say 20 min, i just have to pack a stash of food and toys.