I've got a clamp on mirror that fits the 2003 Savana van. Not quite big enough to see behind me but good enough to feel comfortable with.
The mirror had some problems holding on on my 1999 Chevy Express van. The bottom lip (area below the bottom of the glass) that the clamp hangs on to was very thin and the mirror would slip at times. The mirror on my current Savana has a much more defined area to hook on to so it fits much better. This mirror is the one with the built in orange turn signal which results in some bottom electonics that provide the larger area below the glass.