tach bracket
I mounted mine under the dash between the ebrake and the hood release. Im kinda anal when it comes to things on my dash and in my windsheild. It saved me from drilling a hole in the top of my dash or making up a bracket.
If not on your dash you could go with a hood/cowl mounted with a waterproof shell.
http://pg.photos.yahoo.com/ph/scamp_of_doom_73/album?.dir=/8484scd&.src=ph
Pics are kinda dark the flash died on my camera.