This was done for us by a friend, and it is moist and awesome. We did this for friends in Australia, but it was hard to find the cedar plank for starters, and the fish was very expensive, as it seems most is all exported.
Presoak, totally submerged plank for at least 1 hour. (We are lucky enough to be beside a lake, otherwise you may have to use bathtub or container large enough to submerge the plank. Plank can be Cedar, Alder, Apple, Cherry, Hickory, Maple, Oak. Can also be soaked in beer or wine, it is the cook's choice. Plank must be short enough to accommodate the barbecue, yet big enough to accommodate the fish.
Preheat barbecue to 350°F.
Place plank in barbecue and allow it to preheat until it starts smoking.
Baste salmon with butter and salt and pepper.
Add chives or freen onions.
Place on plank with skin side down.
Barbecue with lid closed for 15 to 25 minutes until fish is opaque,.