RAM mounts are a great way to go. I made the tank bracket but you can find them for sale on Amazon and eBay for about $30 delivered. Almost no vibration if mounted to the gas tank. Mine still lets me use a tank bag if I want to.
I used the normal suction cup mount on the windsree, put a piece of foam tape on top of the dash, and support the GPS on the foam tape as well. Doesn't move, shake or fall of (yet). Easy to see as it's just a low glance down from the road, and you can still see the road when you look at the GPS. I have a stock windscreen, no vent and it doesn't or hasn't gotten rained on (yet).