I am considering a new GPS unit for use off-road in a Ranger. I've used a Garmin Street Pilot for many years for navigating roads and love it. I was wondering what the experiences of others have been using them off road. Is a handheld or dash mounted unit best? Is a larger screen worth the extra money? What units take the abuse and vibration of off road use the best? What units have the best maps? Is the terrain illustrating feature helpful? Any favorites of those more experienced would be helpful. Thanks for any help.