I used to be a huge star wars nerd, but migrated over here due to no more star wars movies coming out. I actually have a full Tusken Raider costume. I think that we need to get a bunch of people who actually have full costumes. People are bound to ask about them, so we just say we're part of the 405th. We could get the word out like that, it should spread pretty fast. I just think we won't get much attention until we actually have a lot to show for (eg. A squad of 10 marines protecting a Master Chief as he goes to pick up his copy of Halo 3.
On a side note, I think we need more categories than Spartan, marine, and helljumper. We can also have officers, crewmen like in the first Halo, AI costumes, and maybe even civilian costumes like Dr. Halsey.