This will help your site get found on google sites under your custom domain, here is some info for you:
Ok go to webmaster central and sign in using your google account
Click on add a site and add the site you want to sumit the sitemap for.
Once you have done this click on the site link on the dashboard page > clilck on submit a sitemap under the sitemap column bottom right hand of the page.
Click on submit a sitemap button.
Type in the box next to your url system/feeds/sitemap
Click on submit sitemap on the right to add it to the list of sitemaps.
.... it takes a fews hours or even days but eventually you will see your sites pages found from the site map when you return to webmaster tools.
Let me know this works for you.