phone-based GPS

Maine,
Are you sure it does not have a GPS in it already? If it does but not maps, I can't begin to tell you how to fix that.
We have given up trying to use the cell phone to navigate. There isn't enough memory to store the maps for a whole day's drive away from the blue roads.
Matt

I'm not following what the screen in your MB has to do with cell gps. I know my Garmin is a POS and the phone works much better.

I trust google on my phone more than the Ford nav. We did have a Garmin 10-12 years ago but found paper maps were more reliable. Did use if in cities they don't move attractions like museums very often.

I see your up East those are not roads they're Indian trails and wildlife paths.

Ok there are APPS like Co-Pilot that are designed for the Big Rig driver. You can tell them, for example. that your "Truck" is 13 foot high and they will make sure they don't route you under any 12' overpasses. I've seen some trucks that were routed under 12' overpasses (or less). Seen RV's so routed as well.
EXPENSIVE

With a Mercedes’ chassis I doubt height will be a problem so the Waze app or google maps should work fine. If your screen will support your phone, there will be a couple USB ports. The vehicle manual should address your screen ability. If so, plug in and open the app.

I’ve used Co-Pilot, all I can say is, don’t trust it! Maybe on a small B it could be trusted a bit, but not for a 37ft class A towing a car!
Stick with the Garmin RV GPS.

I think most folks who use GPS don't examine the route carefully before they set out. They just enter start and stop locations and blindly follow the route. When I plan a trip, after doing the above, I zoom in on the route and make changes to it as I deem necessary, such as bypasses or alternate routes.

I DO use Co-Pilot on my tablet and have found it to be pretty accurate. However, there are times it will do goofy things, but having closely examined the route before hand, I make the necessary correction. It then corrects itself.

Never trust any gps without verifying the route before leaving. Over time I have used Streets and Trips on a computer, two different Garmins, Google maps, and several built-ins. And all have made errors or poor recommendations in directions and destinations at one time or another, some major.

Moved from Tech Issues to Technology Corner.

Aren’t they just saying that rather than have a built in gps and program that will become obsolete they have you use your cellphones gps and app programming do the navigation and display it on the car screen. More and more cars are just providing a smart terminal that connects to the phone for music gps etc, without any built in programming. That allows you Replace the phone and get new capabilities. Also you can select the gps app you want and trust not the one built in.
I can’t imagine any phone that would be disconnected from the internet for an entire days drive or not have the capacity to download it all. But I guess a few carriers or cell phone are still like that.