I guess you could do it there as well, yes, but I have it in the custom-doc class as that's where the current "minimum" is referenced and my site lines up nicely using custom-doc class according to the person who was using the wide-screen. The menu will not go completely across if you use the custom-doc class and the body of the page is limited to 1024 with the background going full width.

Here it is on a wide screen (thanks, Ramius!):
http://webgeek-design.com/images/df2videos.jpg