For 300 - I would probably cut the salmon into service sized portions before cooking and leave the skin on.
Chaffing dishes will probably be OK as long as you stack each layer perpendicular to each other and let folks use tongs.
Finally, use wild caught Alaskan salmon - preferrably Coho/Silvers that are fresh. Being lower in fat content and fresh - they should hold their shape better than other species. If it is frozen - then the species won't make THAT much of a difference.
And please - for the love of God - don't use Atlantic or farmed salmon. I would prefer Chum/dogs over that (and I equate chum to be the 'carp' of salmons).
I would also use a rub that was fairly heavy in brown sugar - as the glaze should also help the fish keep its shape for serving.
After tasting my vegetarian/turkey bacon MOINK balls: "I will die before I become a vegetarian"
1 - WSM, 1 - ECB, 1 - Char Broil Performance Series Grill on Deck, 1 - 18.5" Weber Kettle, 1 - Propane grill/mini-fridge combo, 2 - Propane Turkey Cookers, 1 - Football Grill, 1 - Rectangular Wal-Mart Special, 1 - Terra Cotta Pig I'm going to call Marvin, & one superfast RED Thermapen