iPhone on motorcycle?

I recently bought the Tom-Tom app for my iPhone; it's my first Sat-Nav and worked quite well stuffed inside my jacket pocket, giving turn-by-turn prompts to me over Bluetooth in my helmet. Less than ideal satellite visibility and not being able to see the additional info on the screen, prompted me to mount it on the bike.

My motorbike doesn't have a lot of cockpit space; no fairing or screen and not much room on the bars, so I didn't think the commercial (and expensive) bike mounts would be suitable. Most mounts I found only held the iPhone and offered no impact resistance or weather protection.

So I looked for a hack-together solution. I ordered an iDry waterproof iPhone case from Amazon, with the intention of making holes in it! I need a secure mounting and ideally be able to charge the phone while on the bike.

iDry waterproof case

It's not clear from the photo or the description that the screen cover is a silicon rubber, fine if it's wet, but difficult to pinch-zoom when it's dry. Not that I'm bothered; it'll be difficult enough with gloves on (more on that another time). I don't like the white either, but it doesn't come in any other colour, so I may have to paint it.

I'm not planning on submerging it, so if I'm careful, any holes I make shouldn't be a problem. Although it's also not clear, from either photo or description, if there was any kind of access port for the connector. There isn't. I'm not entirely sure how I'm going to get power into the box in a robust, weatherproof way. Let's get it mounted first, but I have to take account of the opening mechanism:

Operation