I have a Garmin GPS II Plus.
I have installed an overhead console in which my UHF is also mounted.
I had a friend manufacture a bracket which is bolted to the front of the overhead console, onto which I have fixed the GPS II Plus standard mounting bracket.
Power is branched from the UHF Radio through a 3 amp fuse.
Note; This method of mounting may compromise road traffic regulations in some jurisdictions (but not in the NT where I live.
Good site and very interesting ideas.