Re: best place to put the scanguage?
At least with our Prius dash, I just put a couple of loops of masking tape on the underside of the ScanGage, makeshift double-sided tape. Then pressed it onto the dash, centred above the steering wheel. I ran the OBD cable around the steering column and up to it.
I meant this as a stop-gap install, but ended up leaving it thus, never using the velcro strips. Occasionally I replace the masking tape loops, maybe twice in a year. It's suprisingly stable, has never fallen off, and the tape doesn't appear to leave any residue.
I'll pull it off and take it if we're parking in a sketchy neighbourhood, then replace, and it seems to do pretty good.