Why do you want to use Android Auto (AA) ? Why not a rugged device like Samsung Active Tab instead of a AA device?
I have done some research in my quest to "the best solution for me", AA device or dedicated Android device.
First; Some might be MRA related, some are not but I read to many issues with MRA with AA.
Second; I'm pretty happy with MRA on my mobile phone. I have almost 0 problems online and offline so I don't see added value to a AA device.
Third; When I'm traveling I have a bigger device (compared with a phone) with me but not as big as a laptop.
So I decided to stay with a dedicated Android device. I't probably going to be a Samsung Active tab 3 or 5 but other brands are also in consideration.
But if you want to buy a AA device you can look into Carpuride or Chigee. In my research they came recommended. Mostly Youtube and some articles i found on Google but I don't have first hand experience.
I know, its not a (direct) answer on your question but I hope it gives you some information.