TT Bracket, Mount and Garmin 2820
My set up is very similar to BobbyC's at post 10 above. Used the TT bracket and the TT lockable cradle for my 2820.
I've hard-wired the power to the switchable supply and the audio (in and out) to an Autocom unit in the cubby hole between the tanks. Cut a small recess in the screen-side edge of the dash to pass the cables through - they have too many plugs and adaptors to pass through a drilled hole. Looks neat enough though.
This is the third bike (previously a GS then a GS Adv) this 2820 and Autocom has been on with differing mounting solutions each time. The only downside is that the TT bracketry and cradle looks monumentally fugly on the 990 - especially when the GPS isn't mounted.