My GPS cradle had been taped and telco-wired to the dash for far too long,
so it was time to move it to a better spot and mount it for real.  The
decision was to still have the unit just left of the MFD because it's
very visible and accessible there.  Attaching it to the vent panel would
bring it well within arm's reach without having to lean forward, too.

[Each picture expands to a larger one when selected]

A mounting screw head would have to land just about THERE under the panel,
but not so far forward as to interfere with the tab from the main dash-top.
Given the internal geometry of the vent panel piece, the options were
actually somewhat limited.

The screwhead and washer leaves sufficient room underneath and forward, and
life is good.  Between the panel and the cradle mount [which is actually the
remains of the suction-cup bracket with a hole drilled through it] there's
another thick metal spacer to prevent the conical piece from flattening.
Above, holding it all down, is a long threaded hex spacer which makes the
whole mess very easy to finger-tighten in.

The first test drive was somewhat disappointing, actually, because all I
could see on the GPS screen was a reflection of sunlight hitting the rear
seat.  So the unit needed to be tipped back up just a bit like it was in
the taped-down position.  I found an appropriate bit of plastic which
actually nests with the ribs along the bottom of the cradle very nicely,
and in it went....

raising the unit up just the perfect amount, but still firmly anchored
against the vent panel so it doesn't rattle around.  The thumbscrew joint
at the cradle's pivot point is actually splined, so once it's tightened
down at the right detent it actually presses the cradle down slightly.
What's reflected in the screen now is the top of the rear seatback and
the lower hatch window, which stay relatively dark.

It looks lopsided, but the cradle bracket in the back is also offset so
all the forces are sufficiently balanced.  And the plastic shim can't slip
out because it's captured against the MFD.  The power/speaker wire passes
around the back of the MFD hump and heads down to the power outlet.

The unit still has a wide view of the sky through the windshield -- no
need for an external antenna.  Where this sits isn't that far away from
where the factory GPS antenna would go, in fact -- and this isn't buried
under the dash surface.

For a portable, water-resistant unit costing an order of magnitude less than
the factory system, a mounting system that worked out so conveniently, and
a sensible user interface, I think this is the only way to go.  Especially
when I can bring the unit inside after a day's drive and dump the "breadcrumb"
track into the laptop.  If I wanted to spring for the topo maps from Garmin,
it would be great for hiking, too.

So, this is what I see when driving.  Nothing is obscured, except perhaps
the "door open" light which I can see from my right eye anyways.  The
gauge panel's cover takes a tiny sliver of road view, but really no more
than the wipers -- I can live with that.  [The paper diagram isn't there
now -- it was in temporarily as a gauge display guide for a car show.]