Here's the GPX files for my planned 3 routes. Anyone is welcome to join 1, 2 or all 3, pace will be moderate especially day 1;
Day 1 - "Official relaxed ride" a River Road loop with Santa Elena Canyon on the way, 110 mile gas range at most. Loop back through the park, take some side roads, whatever.
Day 2 - Through the Terlingua ranch to the East park entrance, Old Ore Road with lunch in Boquillas del Carmen (bring your passport). After that, dealer's choice if there's any afternoon left. Again, about 120 miles of gas needed.
Day 3 - I'm thinking about staying over Sunday in Alpine, maybe parking in Marfa that morning & riding Pinto Canyon road to eats in Presidio. Slab on the way back. Gas in Presidio so 80 mile range is sufficient. Open to suggestions here.
Edit; these are Tracks not Routes. Some GPS units will not support these, if you have that problem buy one that does or let me know & I'll make Routes for you.
Instructions for using Google Maps offline as a backup are here -
https://support.google.com/maps/answer/6291838?co=GENIE.Platform=Android&hl=en
Remember, if your phone is hunting for signal while you're happily riding you will run out of battery very quickly.