making a sculpted cake for a friends bday. Bottom layer is a history book, then a football helmet and a baseball hat on top. To give you the scale the helmet is made with ball pans and the hat is 1 side of the ball pan. Do you think I need to go with a wood based armature or should I be alright with some stragiticly placed skewers? Everything will be covered in fondant and I plan on assembling on location so I don't have to make something that will stand up for transport.

I don't think you'll need any complex armature. However, even though you're assembling on site, I'd recommend using a sharpened dowel driven through a 1-inch or thicker base board. You can 'thread' the tiers over it.