Dedicated motorcycle GPS devices retail from around $600 or above.

I have an iphone which I could mount in a lifeproof case on my bike, but I'd prefer a dedicated GPS that I could leave on the bike.

The idea of modding a standard incar GPS like a navman or garmin sounds like a doable exercise.

GPS must have bluetooth so rugged and waterproof handheld hiking GPS' are out of the picture.

Any ideas would be gratefully appreciated.