Dadge Caravan is comfortable.
John, sounds fantastic. Having the fridge, rather than a cooler, makes all the difference. Just make sure you drive enough each day to top up those batteries. Check up to see if the extra battery feeds off the car battery. In my Ford it is installed so that it can go flat, but cannot drain the car battery. Otherwise you may find that the fridge and any item you power through the inverter could flatten both batteries.
In 2009 my friends loaned me a Dodge Caravan, which we converted to a 'camper'. Mattress on the floor, 12v mini cooler - didn't even have a second battery, but did not often run it overnight - and a campstove. Served me well for almost 6 months. Took me to Alaska and back. Averaged around 26mpg.
No doubt the bed will be on a frame, with storage underneath. When the seats are removed, the floor is pretty well flat. It also has great headroom. You will be very comfortable.
Lifey
BRP in four days should be OK.
Yeah! John, the BRP is slow going, which I know you don't mind, but it will take a while. Not to mention the numerous view points, which on a clear day allow for spectacular views. You'll love it for photos. Hope you don't strike fog. There are also many short hikes to be had.
I have never done the whole lot at once. I have been on various sections of it, and always underestimated the time it would take. Or maybe I just stop too often. Four days should see you fine. The good part is, if you find yourself way behind schedule, there is a faster road, not all that far away.
On another note, here is a website which was brought to my attention not all that long ago. A lot of great information and hints making the most of living in a vehicle. They also have a very active forum. The whole site, and forum is oriented to country roads and free camping. You might find some of it interesting/useful.
Lifey