I've got a Garmin 76csx that I put in a RAM mount. However, due to my own negligence I almost lost it one day....I now use a lanyard and attach it to my handlebars just in case I'm stupid enough to make the same mistake.
Used correctly, the RAM mounts are awesome.
I've also hardwired my gps to a remote control car battery (7.2V, 1150 mAh, NiMH) underneath the hood, where it stays warm. This gives me a loooooong battery life and no concern of tapping into my sled's electrical system, while also providing continuous backlight display (only way to get continuous backlight is through external power).