Apache URL rewriting in reverse proxy

This is how I got it to work. As well as the changes as per my comment to my original question, I needed to exclude .js and .css from the rule that added a trailing slash.

<VirtualHost *:80>
    ServerAdmin admin@localhost
    ServerName mydomain.com
    ServerAlias www.mydomain.com

    ErrorLog ${APACHE_LOG_DIR}/error.log
    LogLevel warn

    CustomLog ${APACHE_LOG_DIR}/access.log combined

    RewriteLog ${APACHE_LOG_DIR}/rewrite.log
    RewriteLogLevel 9

    Alias /images/ "/var/www/images/"

    RewriteEngine On

    # rewrite rule to prevent proxy exploit
    RewriteCond  %{REQUEST_URI}  !^$
    RewriteCond  %{REQUEST_URI}  !^/
    RewriteRule  .*              -    [R=400,L]

    # consolidate non-www requests onto the www subdomain
    RewriteCond  %{HTTP_HOST}    ^yourdomain\.com$
    RewriteRule  ^(.*)           http://www.yourdomain.com/$1  [R=301,L]

    # Add a trailing slash to the URL (ignoring images, CSS and JavaScript)
    RewriteCond  %{REQUEST_URI}  !^/(images)(.*)$
    RewriteCond  %{REQUEST_URI}  !^/(.*)(.js|.css)$
    RewriteCond  %{REQUEST_URI}  !(.*)/$
    RewriteRule  ^(.*)$          http://%{HTTP_HOST}$1/ [R=301,L]

    # proxy to the Jellyfish server (ignoring images)
    RewriteCond  %{REQUEST_URI}  !^/(images)(.*)$
    RewriteRule  ^(/.*)$         http://app-server:8181/jellyfish$1  [P]
    ProxyPassReverse  /          http://app-server:8181/jellyfish/

    # suppress mod_security rules that were giving false positives
    SecRuleRemoveById 981059 981060

    <Directory "/var/www/images">
            Options Indexes MultiViews FollowSymLinks
            AllowOverride None
            Order allow,deny
            Allow from all
    </Directory>

</VirtualHost>