It is possible to use GPX files, or GPS Exchange files, to quickly import track data and waypoints into an Android GPS app. This example will show you how you can do this in BackCountry Navigator.
In this example, I found a GPX file for Zion's National park here:
I've put this GPX file on my Android phone storage card. To do this, you may need to mount the storage card for your desktop computer, then unmount it when you are done.
I can use a file explorer, like Astro file explorer, to find this GPX file on the storage card's file system.
Clicking on this GPX file will start the import process for the BackCountry Navigator GPS app. You can name your trip file, which will hold the waypoints and tracks from this GPX file.
This GPX import is in progress on your Android for a minute, and then it starts BackCountry Navigator app with this trip file opened. If the GPX file has boundary information, it will center on this, but you may need to zoom out or in, to see the data.
Another helpful step is to download some topo maps or aerial photography for offline use. This ensures you have a map data when you don't have cell phone coverage. You can start by marking rectangles with the selection button, and then use the download button to choose the map sources and detail.
Here we are choosing MyTopo.com at a max detail of zoom level 15, the default. The download of map tiles is soon in progress.
Once this download completes, you will have some detailed map data for the area of interest to complement the waypoints and tracks from your GPX files.
In this way, GPX files can be used successfully in planning and preparing for trips using Android GPS software.