When my Garmin 2720 was in it's slow death I started looking for it's replacement. I didn't want to spend as much money as Garmin wants for the Motorcycle specific GPS so I was looking for alternatives and this is what I selected. I purchased a Garmin nuvi 1490T with a 5 inch screen. To make it all weather capable I purchased a Ram Aquabox 6, this provides a touch through waterproof membrane that works with GPS units but not IPods. The Aquabox also comes with three foam spacers to adjust the depth of the box so you devise fits flush with the membrane. The 1490T fits well in the box and has about 1/2 inch of clearance all the way around it, all of the spacers were used to get it at the right height. I cut a passageway in the foam to allow for the power cord to come in through the back of the box. I also used an extra piece of foam to act as a shelf for the bottom of the GPS to center it in the box. I have now been using this set-up for two months and it works really great. There have been no leaks that I have been able to find yet even during the rain storm we had while supporting the Face of America Ride. The total cost for this setup has been about $250, much less the the Motorcycle GPS's.
When you are sitting on the seat, none of view of the dash is blocked. (BMW R1200RT)