Back Country is what a lot of people use, I haven't tried it. I have seen people use plain jane garmin Nuvi's, the kind you use in a car or truck, event though they are not water proof. They will mount them out of harms way, or just stick em in the glowe box until they need it. I started using a garmin etrex 20, but it is definitely awkward with such a small screen.
I use a Garmin Oregon, but the screen is small. He asked what app for his phone and BCN would be my choice there. I am watching flea markets and such for a used tablet so I can use BCN. You can get waterproof cases for nearly any gps or tablet