Go to Garmin.com as they have accessories for them. I have an eMap and bought a nifty dash mount for it that is small and easily detaches. It's far better than the local universal types are. They also sells eMap mounts for bikes as well.
If reception is a problem, you can get a roof mounted magnetic antenna too (not cheap but...). I finally bought one as it helped with satelite reception which would occasionally fade w/o it in my car.
As for location, w/o the external antenna it has to be on the dash or it won't receive and it works better in some cars than others depending on the glass. I used mine in a rented Jeep when on vacation about a month ago and didn't need the remote antenna in that vehicle. It's fussier in my Volvo w/o the roof mounted antenna.