Ended up just using my phone for navigation, and even though I was recording GPS and heart rate the whole time, I'd only used 50% battery after 14 hours riding. Nice.
There was another guy at the campsite who was looking for someone who had downloaded the route. I AirDropped it to him, and he transferred it to his Wahoo bike computer with no trouble.
For shorter rides/runs, I use the WorkOutdoors app on the Apple Watch. It's only battery life that's an issue when the activity is longer than 6 hours. Just this morning I had the opportunity to go for a run a bit out of my normal zones, so within a minute I had sketched out a route on the phone and transferred it over to the watch. (That some of the paths I'd used didn't actually exist anymore was a separate issue, but I've already updated OpenStreetMap to fix that.)
If they could fix this one problem, I'd buy more of their sports-oriented watches, but this is the one thing that I find really hard to deal with.
Otoh, the watch is phenomenal and beautiful, and I love having a watch that lasts 5+ days on a single charge and looks like a normal watch, but tells me my calendar and such, and can be used to track running and hiking.