Just noticed that eval_sidebar function could do with it's own fallback, in case the global isn't set by one of the pages - for example, on my 404 template I don't really need to worry about calling the eval_page function. So I've adjusted the eval_sidebar function to be:
function eval_sidebar() {
global $eus_page;
if ($eus_page == NULL) {$eus_page = "Default"; } // If no global set, then set the page type as default
return $eus_page;
}
Again, don't know if this is the best way to do this, but just in case I miss a template it's good to know it will fallback.