You can add your RSS feed as a sitemap, but it will contain only the last 20+ items (different from a real sitemap, which contains all of the pages), which is IMO all that you need. PS: You can also add your RSS feed as sitemap if you are using Blogspot blog. Just for informative purpose.
I am about to make a php script that gathers the post_names or IDs from the MySQL table "posts" and drops them as file names into my existing sitemap. But then I have a dilemma. If I use post_names, the sitemap entry will look like: domain.com/keyword-blog/this-is-the-title-of-the-post You see, a bit worrying, isn't it? It contains five or in some cases even 8 hyphens. Maybe it is better to use post ID? In this case the entry is domain.com/keyword-blog/post_id=1? or something similar. What's your opinion? I too advise against plugins. I've heard from some webmasters that automatically generated sitemaps are sometimes rejected by GG!