I've seen alot of mounting options and custom stuff here and elsewhere but it always seems like overkill to me when it could be so much easier and light weight. So I'm gonna share my set up. I'd like to start off by saying I've been known to ride like an animal on-road, off-road, off the trail, through my back yard, wheelies, stoppies, high speed, you name it... and I also have my super cool slow days out cruising. This set up has NEVER failed me in any of these scenarios. Now I know for sure I don't have Harry the homeowner cheapo tywraps so just find yourself some good profesional quality ones and carry one or two spares just in case, altho I've never needed them for the GPS mount. In the following link I don't see all the parts that came with the mount so here is what I recieved.
Handlebar mount parts
Rubber tape - for handle bar protection and mount grip.
Straight mount - for level mounting
Angle mount - for mounting on the rise/angled section of the bar
Tywraps - 2
Handlebar Mount <-- Link
The GPS unit itself was the cheapest one I could find at Staples about 4 or 5 years ago. It's a Mio C220 and it uses the universal holder that connects to the mount. It is NOT water proof so I also carry a plastic sandwhich zip-loc bag in case it rains. If I was worried about wrecking it I would just remove it and stuff it in a pocket but so far I think I'm up to $150 here. About $30 a year ,no problems to report and as much as I love it really I've got my moneys worth and I don't worry about it for a second during the rides. The map and options are exactly what I was looking for. Big plus is the touch screen works with my riding gloves on. I've owned one other GPS a tom-tom that I paid $600+ for and the Mio is what I still gravitate to. Again it uses this universal mount that just holds onto the unit with 3 spring loaded fingers. Flawless grip.
GPS Mount <-- Link
And again for this I don't see all the things that came with mine or maybe it has changed. It's a nice set up where you push and twist the mount which relieves itself from the handlebar base. Even if it doesn't come with the twist lock anymore I have just snipped the two tywraps and off ya go.
For power I have a Battery Tender already installed and it has the charging lead with waterproof cover sticking out from under the seat. Deltran sells a cigarette style female lighter socket that fits right into this. Wiring couldn't be any simpler. This item also has a water resistant cap when not in use but with the ease of installation you could just remove it if you're worried about extreme water issues. Did I find this before I fabricated one from a leftover Bettery Tender accessory? Nope, lol. Your build will be that much easier. I avoid the rain but I trust my setup if I was caught out in the worst. I've tywrapped this female adapter to one of the metal frame tabs inside the glove box under the left hand side fairing. Factory made adapter here...
Female Cigarette Plug Adaptor - Accessories - Batterytender.com <-- Link
If you don't already have a Battery Tender installed get one or just get this...
Battery Power <-- Link
Stick your "car" charger male cigarette charger into it. Mine was actually for my phone because it has a cool red light on it for that cheapo bling and has the spiral spring type cord so it's nice and tidy and flexable so it doesn't interfere with the steering in any way. One loose wrap over the top of the handle bar and plug it into the GPS. Off ya go.
Pictures to clear up my ramblings ...