I think you have the meaning of :trailing_slash => true
wrong.
All it does is add the / to the end of you path helpers. No redirecting involved.
Your routes will still respond to both with and without the trailing slash.
If you want to redirect all non-trailing_slash
uri's like /download
to /download/
using a nginx http server you would do something like this:
rewrite ^([^.\?]*[^/])$ $1/ permanent;
You would still want to add the :trailing_slash => true
to your routes so your path/url helpers generate the the correct uri's (so user don’t need to redirect).