Here's my solution, although I can only afford a 296. I put a big wide
strip of some industrial strenght velcro on the back of the unit and
another on the right "glove box" door. I don't know how many g's it
can pull but it would be significant. However, I usually just lay the
unit out of the sunlight in the right seat or on my lap so I can see
the screen better.
Electrics are handled by installing a cigarette lighter socket,
legally, and using the lighter plug provided with the GPS unit.
P.S.
Don't wet your finger and stick it in the lighter socket.
Bart