There's probably dozens of ways to cedar plank salmon on the bbq, here's one way to do it:
Walk over to your cedar fence with a saw in hand. Or better yet the neighbors fence.

Cut a piece that's about a half inch thick and as large as that will fit on your grill.
I have both a gas fired Webber and a charcoal Webber. I always use the charcoal. But that’s just my personal preference.
Once you have the cedar plank and you are sure it will fit on your grill, find a water tight container that the plank will fit in. Put enough water said container that can cover the plank. Add plank, making sure the water completely covers the it. Otherwise it will warp.
Now comes the hard (but fun) part.
Tell the wife she has to go with you to Tillamook, or Waldport, or Newport (or wherever) and catch a salmon so you can bbq it and all can eat like kings. This makes her feel like part of the team. Good for the marriage. If she refuses, then you have some options. You can go catch the fish yourself, go to Safeway and buy the fish, or you can do what I did. I got a new wife who wants (if it’s possible) to fish more than I do! Coho preferred here, but Chinook will also do.
After catching the fish, bonk it

on the head then bleed it out and put it on ice. In short take very good care of it.
Upon your return home, while the wife is filleting the salmon go ahead and fire up the grill. Make sure she leaves no bones for the kids to choke on. When you have that done, take the still soaking cedar plank out of the water and dab it lightly with a paper towel. Then rub olive oil on the smoothest side. By this time, the wife should be done filleting the fish. Have her put one of the fillets away and take the other. Then have her start filleting the other fish. Put the filet on your (now) oiled and water soaked plank. Rub olive oil all over the fillet, then shake onion powder, garlic powder and whatever else you make like. Also put fresh lemon slices on it. The more the better. Spread out your coals and put your soon to be dinner on the grill.
It should like something like this:
Close the bbq. While the wife is filleting the rest of your catch have a cold beer.

If she happens to finish before dinner is ready have her start cleaning the boat. Set the table for a dinner that should make everything up to her for having to fillet all of the fish.
About 15 to 20 minutes (depending on how hot your fire is) it should be ready to take off the grill. While it’s cooking don’t be surprised if the neighbor(s) show up (especially in the summer) to see what smells so good and perhaps ask what happened to their fence.

Don’t admit anything! Tell them you are trying to cook up a carp the wife caught on the Willamette or something. Or better yet, tell them to go away, just don't admit to anything!!
It’s done when the juices are kinda bubbling on the board. Word of warning: DO NOT OVERCOOK!!
Get another cold beer and enjoy!

Happy eating!