I had a bit of a quandary trying to figure out how I could hold my Garmin GPS. I tried a few quickie ideas when canoeing this last year while on out on the water, which is about the time I discovered I had the problem. Not a lot of success.
But now, I've come up with an extremely easy solution. I mount it to my thwart!
1. Install the back plate that has the webbing and the carabiner.
2. Remove just the carabiner.
3. Slide a 6" bungee with a ball mounted (for tarp purposes) folded, through that hole.
4. Wrap it around forwards. There is just enough tension to hold it in place nicely, without breaking the GPS.