Military care package ready--what are the mailing procedures?

I've got a military care package for my friend who is stationed in Kuwait. I've never sent anything to a military base before. Do I need to leave the box open until I get to the post office for inspection or can I have it taped up and ready to go by the time I take it to the post office? When do I fill out the customs sheet? I'm uming since it's flat rate they won't need to weigh the package. Also, should I fill out the address to my friend on the box or will they type up a label with her name and address and also my name and address when I pay for shipping? I'll have my driver's license with me: is that enough for identification? Will they even make me show an id? Thank you.