I cooked them on my gas grill. The thermometer that came on the grill was reading 400* - 425*. I'm not sure how accurate that is I have never checked it. I soaked them for about 4 hours and they caught on fire in about 10 mins or so. I had to spray them with water to put the flames out. Next time I will turn the heat down a bit or turn 1 side down like africanmeat mentioned to try not and burn them so bad.
I have heard you can reuse just rinse off with water, (no soap) and wrap in plastic wrap and put in the freezer until you are ready to use them again. Mine are pretty burnt up so I will probably throw them away and get new ones next time.
I always cooked salmon right on the grate also, I put the fillets on skin side up for a few minutes to brown and give nice grill marks, then finish them skin side down, but these were a Christmas gift so I thought I would give them a try. Also I always thought cedar was poisonous. Reading online it says western cedar is ok but don't use eastern cedar it is toxic if anyone is thinking about buying it from a lumber yard. These were from the grocery store so they are safe to use.
My mother thought it was the best salmon I ever cooked and the wife said it had a really good flavor, but she likes the golden brown crisp when I put them straight on the grate for a few mins, before cooking skin side down.