There are quite a few results for add trailing slash .htaccess on Google, but all examples I found require the use of your domain name, as in this example:
R
This should work:
RewriteEngine On RewriteBase / RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_URI} !example.php RewriteCond %{REQUEST_URI} !(.*)/$ RewriteRule ^(.*)$ http://%{HTTP_HOST}/$1/ [L,R=301]