Here's my setup. I sold the BMW mount that came with the Nav IV and purchased a Touratech locking mount and adapter. I like it bc I can also mount my RD on top.
I used zip ties to run the cables and velcro to hold the RD in place (plus the flimsy metal mount).
The big plus of the Touratech (other than it locks) its that -in combination- with the adapter mount) brings the GPS closer to you so there is no far reaching when you need to press a key while on the go. Its still on the firld of view but it is not obtrusive.