Enclosing all content exactly within a div

Hiya Tom + others!

I'd like to enclose all of my site (header, nav, content, footer etc) inside one div, that's exactly the size of the site content's outer edges.

I've started by enclosing everything between "Before Header" and "After Footer Content" in a div with GP Hooks.

What's the CSS needed? I'd need this new div, call it .allwrap, to have the width of it's children - whilst not having IT define the width of it's children.

Am I going about this in a bad fashion?

Thank you.

- JP