How to force trailing slash?

@jenstornell:

I can save content from the panel with the following condition:

# make panel links work
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^panel/(.*) panel/index.php [L]

# remove trailing slash, but not for the panel
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !^/panel/.*$
RewriteCond %{REQUEST_URI} (.*)$
RewriteRule ^(.+)/$ http://%{HTTP_HOST}/$1 [R=301,L]

# make site links work
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*) index.php [L]