Update: My original post was out of date so I have deleted most of it.
This case I have been using now for 4 years. It holds my Garmin 760 GPS and a battery pack that powers it for about 9 hours. It is a fantastic solution for motorcycle travel. Renting a motorcycle you can simply and quickly strap on your navigation, no wiring and be underway in no time. end of day recharge your battery pack and ready to go again. I have used this is rain and it is waterproof no issues. You can operate the GPS through the plastic no problems (but not a phone which is not pressure touch operation) I now have the revised model 4 of this case from same manufacturer and it is even better.
Some of original post below:
This is a iPhone GPS solution for motorbikes developed by WikiMobi called SoEasyGPS. The system works like this, the case has a waterproof outer that you remove to access the main case itself. This has a waterproof zipper and two compartments inside the top is for your iPhone (GPS) and the lower is for a backup battery which feeds your iPhone thus eliminating the need to source power from the motorcycle.