Issue with non-www redirect (302 instead of 301)

[contempoweb]

I have PS 1.5.6.2 installed in a subfolder of my domain (www.mydomain.com/us/)
I have friendly urls on, and in"Preferences > SEO & URLs" my shop domain and ssl domain are set to www.mydomain.com and the base url: /us/

When checking the redirect of non www (http://mydomain.com/us/ -> http://www.mydomain.com/us/'>http://www.mydomain.com/us/) It shows that it is a 302 redirect, but I would like it to be a 301 redirect.

So I have tried adding a redirect to the very top of my htaccess file:

RewriteCond %{HTTP_HOST} ^mydomain\.com$
RewriteRule ^us/$ http://www.mydomain.com/us/? [L,R=301]

The problem here is that http://mydomain.com/us/ then redirects to http://www.mydomain.com and not as intended http://www.mydomain.com/us/'>http://www.mydomain.com/us/

How can this be resolved?

Thanks!