I need #megaAll (gray), #megaMain(pink), and #contentContainer to extend all the way down the page, but it seems unable to extend to the full height because of the scrolling on the body. I need the scrolling on the body and fixed sidebar on the right to remain.
Extending them down is just height:auto; which need not to be mentioned as it is default. Whatever will be the height of your body, it will auto adjust it all over the page.
"sidebar on the right to remain" means fixed, this will work if I got you right.