As the woocommerce plugin does not work together with singl for a couple of pages (e.g. the single products page) it took me a while to figure out how to solve the problem. By adding this code to the "wrapper-start.php" of the woocommerce plugin it all looks perfect:
case 'singl' : echo '<div id="primary" class="content-area"><div id="main" class="<em>post-2 page type-page status-publish hentry</em>" role="main">'; break;
The exact code of the italic part can be copied from a normal posting anywhere on the existing singl page. The woocommerce pages are then in centered and in the white frame, just like the rest of the page.