I was actually able to solve this very easily with tasker for anyone interested.
Well a combination of tasker and an app called secure settings actually.
My watch now remains connected for notification and audio connects to the truck automatically. Once I leave the vehicle everything returns to the watch.
*1. Open tasker and click the "TASKS" tab
*2. Click the + at the bottom right and give the task a name such as "Connect Car Audio"
*3. Click the + at the bottom right and select Plugin - Secure Settings
*4. Click the Pencil icon at the right of configuration and select Actions - BT Connection
*5. On the drop down select your vehicle
*6. Press the CONNECT/DISCONNECT button so it displays CONNECT
*7. Press the floppy disk icon to the right of BT Connection
*8. Click the < at the top left next to the tasker icon. You have now configured the task!
Now to create the profile (or the trigger that will run the tasks):
*1. Click the profiles tab
*2. Click the + at the bottom right and select state
*3. Select Net and the BT Near
*4. Click the magnifying glass on the right of Name and select your car bluetooth system. If you prefer you can select the address rather than name.
*5. Select the option "Standard devices"
*6. Click the < at the top left next to the tasker icon.
*7. You will now see a list of tasks to choose. Choose the connect car audio task (or whatever you named it).
In my screen shot below you will see that I created two profiles.. the second one is not necessary, it just gives me a notification that my phone HAS connected to my truck.. (Which also comes through to the watch) I mainly did this so I can monitor that this is working, but I may remove it at a later date. It seems to connect perfectly every time as it should so I really don't need to know about it.
I'm all fairness I borrowed some of this tasker prowess from a post on redit but I removed a bunch of steps because they were simply not needed, and actually it works better my way. The original version has a prior task of telling tasker to disconnect from the watch and then power cycle bluetooth before connecting to the vehicle.. I have no idea why, but the end result of that is not being connected to the watch at all when in your vehicle (no notifications) and also having to setup exit tasks so it would reconnect to the watch on exit.. if that's what you prefer go for it, but my way the watch remains connected and you still get your notifications, only phone audio is routed to my truck which is exactly what I wanted.