gphnl Is there any workaround at all to get a map app working in the car's android auto system?
Android Auto (AA) can be made to work with apps installed from outside the Google Play Store (the apps themselves will still need to support AA, but Comaps and Organic Maps do).
To do so, go to AA settings in Settings > Apps > Sandbox Google Play > Android Auto > Android Auto Settings. Then scroll down and tap Version 8 times. It should give you a message about enabling AA developer settings; accept it.
Then, tap the three dots in the upper right corner; it should list Developer settings there. Go there, scroll the list until you find an option that says Unknown sources. Enable it. That will allow you to run apps in AA that have been installed from outside the Google Play Store.
Hope this helps.