To get the route on strava, use desktop version (html version) and "star" the route. Once starred, magically it appears on the phone.
Go to Record page within the app, on the top left you'll see the option to choose Map view (swipe right or click that) & then click on select route. Your starred route would be there. To use the route while riding one just needs to click Use Route within the app.
Please note that this is a self supported ride, all riders will be subject to scrutiny to make sure they are able to ride this long distance. This is not a race, its a ride.