Radio Shack is closing out a couple of models of gooseneck cellphone mounts for $10 each. Possilby because their suction-cup bases scared away customers (it sure gives me the willies to think about an expensive cellphone or PDA being mounted with one).
If you use a nail or screw to tap out the pin holding the suction cup release lever, you find a hold that you can put about a #10 or so screw through to attach the base firmly. The previous owner of my truck had attached one of those slide-out mounts for a CB to the roof. I finally found a use for it: I screwed the mount to it, and it holds the Z in a position where it's out of the sun, out of my normal line of sight, and easy to see when I want to.
To attach the Z to the cellphone holder, I took the holder apart and removed the "gripper" mechanism (which doesn't spread quite wide enough to hold the Z. Dammit), and tie-wrapped the "Strongarm" bracket out of a Case Logic case to it. I drove around for a while to make sure the idea was going to work, and it did. So I'll drill a couple of holes and screw the bracket to it.
I don't know how the stiffness of the gooseneck compares to the new models, because I'm too cheap to spring the $25 RS wants for them. But it's a lot better than the microphone gooseneck RS sells, which flexes too easily for vehicle use. I put a 90-degree bend in it to hold the Z vertical with the base mounted parallel to the roof, and it doesn't seem to flex visibly at all. Even in my "camper special" pickup, which rides like a buckboard if it doesn't have a ton or so of load on the bed.
So, for about $25 ($10 for the mount, and $15 for the case at places like Fry's and Circuit City) and very little work, you can make a really solid mount that fits the Z very well, and is probably even solid enough for off-roading.
fwiw: I dunno whether it was just the particular units I got, but the model for fliphones (with a clear phone holder) was easier to remove from the gooseneck part for tinkering. I was afraid I going to break the plastic when I whacked the larger one to disconnect it. That may be "better" or "worse", depending on whether your goal is to have a system that's "extra safe" or "easy to mess with" ;-)