Have you looked into a marine application, I would think a radio for a boat that would take the abuse of the pounding of the waves and humidity should work on the bike.
Here's a wild shot. Have you checked your fairing brackets? They are known to break. It's not always easily noticeable, but does cause a lot of vibration that could be causing radios to fail.
There was also a bulliten about the radio hitting the stearing head retaining nut.