Pirate36,
It does seem intuitively odd to catch a bottom lunker, like a grouper, by trolling as I had always thought that you catch the fast-swimming pelagics by trolling. But it does work.
You need to first, and most importantly, being fishing in a place that has grouper that ain't too terribly deep. In Tampa Bay, the water depth is 45'.
I troll 2 or more lines at a time. I use planers (but downriggers would be easier) to get the soft "Storm" lures down to the bottom. All 8 of my groupers last week were caught with these. Others use Stretch Manns (30s and 40s) without planers and I will try these again, although I have not had luck in the past. I troll at 4 - 5 knots and try to keep the lures less than 5' from the bottom. Occasionally they get snagged which trips the planers and requires that they be reset, which is no big deal if you know how to reset them.
IM me if you have any specific questions.
Richard