Update from my earlier post with the GoPro. I'm now using two Garmin Virb XEs. These are great cameras, good for much more than Mapillary. I still rely on the GoPro suction cups because they're the best ones out there, in my experience. I don't use the tether anymore though, as the charging cable acts as a bit of a tether. I suppose this is risky, but I've never had an issue. I've seen videos where this suction cup is stuck to the side of a rocket, so I think it will stay stuck.
Here are some photos of the Garmin Virb XE on the front, and then on the side of the vehicle. The front of the hood works best for the front view, and the side window is great for side view.
Front, close up
It is waterproof