Personally, I'd use mod_rewrite to append the / to any URIs that don't end in an extension from a defined set - probably \.(html?|css|jpg|gif|png|ico)$ - rather than having Catalyst do it, on the assumption that anything handled by Static::Simple will be ending with one of those extensions.
Comment on Re: Catalyst - Add Trailing Slashes to URLs
By default you are correct, but adding [R] to the end of your RewriteRule will cause it to do a client-side redirect instead of handling it internally.