Hello! I actually cosplayed as Bossun this past Otakon and it was a lot of fun to do so. Because I am tall I also cosplayed as Mori-senpai from Ouran Host.
Making the hat was really easy. What I did was took an old cap and cut the visor part from it so what I had remaining was the top part or the dome. I then went to Staples to buy a RED book sock cover. I just folded the sock in half so that one side would have the two corners of the cover sticking up (the ears). Plop it on top of the hat an walla. Your done. I also cut out two cone shaped cones from cardboard to help the ears stand out. I will send a picture as soon as I find them. All you really need to do is have the book sock and hat and the helmet is really easy to put together. I hope this helps!
Feel free to add me on Facebook if you need more tips!
Minami Ikki "Karasu" - Air Gear --> Otakon 2007-2009, Tendokucon 2008
Takashi Morinozuka "Mori" - Ouran Host --> Otakon 2010-2011
Yusuke Fujisakii "Bossun" - Sket Dance --> Otakon 2011