Otterbox seems to be the only product available for the Lumia 920, and even then it is only a “dustproof and shockproof” box, not waterproof. And worst of all it has not handlebar mounting option. Some serious hacking was required.
(Mr Otter if you ever get to read this, my version of your box is a lot more useful than yours! Please consider…)
1. I waterproofed the box by sealing up all of its (many) orifices. I put a USB cable in place, smeared it with olive oil and glued around that. So I can insert or remove the cable and it’s still a very snug fit.
2. I broke the silly belt clip of the bottom of the outer housing, and replaced it with a generic handlebar mount.
This setup has not been put on a bike yet. First time will be in Borneo.