Err... Does that GPS thingy in that thread even work? At least it must get a bad reception at some places...
Anywho, I just drilled a hole and used some special stuff that I don't remember the english word over.... You basically drill a hole for it, put it in the hole, put the plastic nut against it on the other side, put the wire through, and screw the other end of it so it tightens to the wires and seals 'em. Works okay, but doesn't look good if it isn't easy to "cover" it behind the roof rack.
That method showed in the thread, well, it's brilliant, until it fails. And believe me, it does. I've seen this and done this so many times at work. And sometimes things don't even last the year. But maybe the weathers are abit more extreme over here along with the salt on the roads 9 months a year. =)
If you like it on the other hand, then go for it, in worst case, you'll have it broken in few years/months and have to fix it or find some other solution. =)
Also, run big enough wires for the lamps and dont ground it on the top, take it down to the engine bay or inside car before you ground it, otherwise you'll have rust problems. =)