Any ideas for a groom's cake (see details)?

My sister is getting married this summer, and has asked me to make and decorate the groom’s cake. It’s a very small, informal outdoor wedding, so it doesn’t need to be crazily fancy or anything. She’s asked me because I made a couple of funny cakes for birthdays before (kitty litter cake with tootsie rolls spelling out the person’s age, and a Yoda cake for Mr. Fiance). She seems to think I have some kind of skill, but I’m really not all that good.

Anyway, I’ve decided that I’d like to have the cake itself in a camouflage pattern, which is easy enough with food colouring. But I need to decide what shape and style to make the cake.

The groom is into video games, so I’ve thought that I might make it in the shape of an Xbox 360, but I’m not sure about the decoration. Does anyone have any experience using ganache or buttercream to create a smooth finish? I’d like to avoid fondant if I can.
He likes military-type stuff, hunting, video games… If anyone has any ideas I’d love to hear them.