Rewrite Rule on apache2 with tomcat6

Question

I am trying to rewrite a request from a GWT-Webapplication, to be more specific: gwtupload. The Webapplication is bound to apache2 via mod_jk.

I need to rewrite the following request:

    http://www.example.com/servlet.gupld?new_session=true&random=0.3840860207955523

To

    http://www.example.com/webapp/servlet.gupld?new_session=true&random=0.3840860207955523

Anything after servlet.gupld? has to be variable.

The Webapp itself works fine and is boud like this:

    <IfModule mod_jk.c>
    JkMount /webapp/* tomcat3
    JkLogLevel error
    </IfModule>

While my (not working) rewrite rule looks like this:

    <Directory /var/www/www.example.com/www>
            Options -Indexes FollowSymLinks MultiViews
            AllowOverride None
            Order allow,deny
            allow from all

    RewriteEngine On
    RewriteBase   /
    RewriteRule   ^/servlet\.gupld /webapp/servlet\.gupld [PT,L]
    </Directory>

For the moment I am always getting a 404 on the request to the servlet.

Can anybody help?