Exactly what he said, and if you get the ram mount for your GPS it will stay on the bike no matter what you do. So far my gps has stayed on through every trail, wreck, and crash I've tried.
The one thing I don't like, is that when you have it plugged in, it's not really waterproof anymore.
And to add, for a simpler method you don't need to use software. just plug the gps in, copy the files with different names, MAKE SURE DIFFERENT NAMES, to not overwrite the original files. Then from the device you can choose which maps to load.
The first time you load the map from the device, it will take a bit to load it. Then it's quick.
I keep a very detailed regional topo on the device, but not loaded usually.