Hello!
Entirely up to you!
I supply 3M Velcro with 300LSE adhesive compound - maximum sticky low surface energy plastics flavour. It is pressure sensitive, so it'll slide around the dash a little but once pressed down that's it, stuck. Peel it off and it won't re-fasten again ever. Works best >20C. The harder it is pressed down, the more it sticks.
Usually you can tuck the wire between windscreen and the dash, or dash and the A-pillar to get behind the dash. Flat section, and less than 3 mm thick. I put a hole through my dash because the MX5 ones sell for about 10 pence (only part of the car that doesnt' rust) and take 30 minutes to swap!
If you're more patient than I am, spaceboard insulation foam from B&Q can be cut/carved with a knife then wrapped with vinyl/alcantara to make a dead neat little pod for dash mounting things. Allsorts of potential there.
You could also flush fit it by sandwiching the dash at the split line. Not designed for this but can look good if you've a flat enough surface. Detail here:
http://www.speedview.co/forum/Thread-Ca ... -dashboard
The film is a one-way tint to prevent ghosting and improve contrast. Its a tint rather than opaque, so is exempt from the MOT restrictions on positioning. (5% transmission one-way mirror tint if you're curious, and no need to keep it that size or shape - I supply large so that instructors and trackday cameras can see from passenger seat)
Cheers,
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Marko
