Paul that’s a great suggestion. I also have a SIMless old iPhone I’m planning to use as a back up phone for OS travel. I hadn’t thought of using it for navigation. 

Yeah - basically that's its only use anymore. To download RWGPS maps you'll need at least a basic subscription, but once you have the maps downloaded, all the routes you created can be downloaded to the phone, and then you're in business. You can't have your screen on full-time as that would just drain the battery  too quickly. My screen shuts down after about 15 seconds, so I basically swipe up to see the next turn, and then after I make the turn, swipe up to see if I turned onto the correct road. Once confirmed, I'm good to go until the next turn.