OK, decision time. After hearing all the pros and cons over using a tablet I've managed to overcome my original bias and go the tablet route.
Years ago I gave my wife a Asus Transformer 10" tablet. She uses it primarily as an e-book reader but does do a bit of Internet news surfing and email checking as we travel but it's slow as molasses on a winter day and I've been considering buying her a more up to date mode. So, I'm getting a Samsung Galaxy Tab A 10.1 for her and will re-purpose the Asus as a GPS unit. I had tried to give it away to the grand kid but no one wants it since it's so outdated but it does have a GPS function.
Still need to figure out the mounting and will try the side window idea and see how that will work. Meanwhile I will need to find a travel adapter and a source of 12V power in that area. I also think I'l just start with the basic version of Co Pilot and make an upgrade decision later if I like it.
Thanks again of all the input this has been a very useful thread and it actually stayed on topic (bit of a shock).