(– by Drizit #6240 –)
good chance you won't need one but it depends on how much free space your gps has. the gpx files are quite small.
Don't expect the best results with a Nuvi, I've been fighting with mine and so far all I can get to show is the start and finish points of the trails but no track. You will need a program called "basecamp" it can be downloaded for free from the garmin web site. Good luck and if you find a way to get the tracks to show up let me know.