The pecentages refer to the imediate parent of the item. The way you have it set up, the mainbody will always be 80% of the wrap, regardless of wheather you publish the right column (#sidebar-2)
and publishing it or not will therefore have no effect on either #sidebar or #content.
To make the right column collapse you can change your template index.php file so it says something like:
if ( mosCountModules( 'right' ) ) {
?>
} else {
?>
if ( mosCountModules( 'right' ) ) {
?>
}
?>
then make a new selector named #main_body_full
in your stylesheet to give the proper attributes for when the right column is not displayed.
Note that you also need to drop your width percentages a point in order to account for the border width.
Also, you have an extra # sign in your ##main-body selector.