I have two little 'mouses' mounted under my panel cover. These have two screw holes on opposite sides for attaching. Thru these holes I would run plastic locking wire ties and around the top tubular panel frame ( S-H Discus ) suspending them in between the frame tubes. They (GPSs) are suspended a few inches apart just underneath the panel cover and have never failed to provide a signal. No glue or tape and easily to removed and replace when instrument work is required.
R