mod_rewrite rules to drop www prefix

I'm trying to write some mod_rewrite rules to drop a www prefix from http://www.example.com and redirect to http://example.com

Using Apache 1.3 and mod_rewrite I have the following rule set for the root of the site.

rewritecond %{http_host} ^www\.example\.com [nc]
rewriterule ^(.*)$ http://example.com/$1 [r=301,L]

This works fine for the root of the site, however I have another set of rewrite directives in the /blog/ subfolder to handle redirects for a wordpress blog so I need to declare rewrite rules in there as well.

For the /blog/ subfolder the .htaccess is

rewritecond %{http_host} ^www\.example.com [nc]
rewriterule ^(.*)$ http://example.com/blog/$1 [r=301,L]

This rule works fine if someone vists http://www.example.com/blog/ and redirects to http://example.com/blog/
However, if someone visits and leaves out the trailing slash, http://www.example.com/blog then the redirect goes funny and appends the local directory structure of the site so the URL looks like:
http://example.com/blog//home/users/xyz/domains/example.com/public_html/blog

Any ideas where I'm going wrong?