I have a Garmin Nuvi 1450 going on 3 years now. Still ticking and love it. 5" screen, not "advertised" as waterproof but I've taken it through it's paces!!! Found a $8 mount on Ebay and works great. No issues. Not bad for the $170 I paid for it directly from the local Best Buy.

 

I bought a cheap Garmin "car GPS" and mounted it to my bars with a Ram mount and have been using it off and on for 3 years on long trips. Works great! If I remember right, the touch screen works with leather gloves on too. Doesn't seem to vibrate much mounted between the risers either.

 

car garmin with ebay/amazon zippered bag GPS mount.
The only drawback i find is that a car GPS like my garmin can supposedly store routes but does NOT store routes exactly as created by the harley trip planner or mapquest.
It requires creation of multiple way points in order to twist arm of GPS to not search for shorter or quicker route than the one you created.