I have a standard GPS, Garmin 205 I think, and I mounted it in one of these:
[ame=http://www.amazon.com/Arkon-GPS032-Smartphone-Waterproof-Motorcycle/dp/B003FMUP0K/ref=sr_1_1?ie=UTF8&qid=1291347512&sr=8-1]Amazon.com: Arkon GPS032 GPS and Smartphone Waterproof Hard case with Bicycle and Motorcycle Mount (Black): Electronics@@AMEPARAM@@http://ecx.images-amazon.com/images/I/51%2BR7EQ6GdL.@@AMEPARAM@@51%2BR7EQ6GdL[/ame]
works awesome, stay dry, cheap!, you can still use touch screen through the cover.