Trailing Slash - 301 Redirect - Google SEO

If you are not familiar with this subject please read this article here:
http://googlewebmastercentral.blogspot. ... er-10.html

I am using VS 1.5.5.1 & what I am trying to do is add a trailing slash after each category by writing a redirect code in the .htaccess file but not after a product url or file name that ends in: .php, htm, html

Also I am forcing the site to redirect to www & not non www & also redirecting
http://www.example.com/index.php to http://www.example.com/

For more info on this go to http://support.google.com/webmasters/bi ... swer=44231

But i have tried every code combination out there to do this, my host says it is the way opencart is built that it is not letting me do this, I cant believe that yet, do any of you have the htaccess code to do this - add a trailing slash after each category by writing a redirect code in the .htaccess file but make an exception for a product url or file name that ends in: .php, htm, html ?

My host says I should for every category add a RewriteCond %{REQUEST_URI} that is not a good way to do this, so any help out there ?

Is opencart's design blocking this from happening ?

Maybe this can be built in to 1.5.5.2 to reduce duplication and have better SEO ?

use your .htaccess file for redirection from non-www to www.

Don't bother about repeated URLs on product page since they already have meta canonical.

So right now you can get at least 3 urls for the same product

domain/catergory/producturl

If I view the product through brand or another category it shows as:-

domain/brand/producturl or domain/catergory2/producturl

So, potentially 3 different URL's for one product. And probably a 4th if you do a search for a prdt & that gives you another url for the same product.

I have tested my sites which are 1.5.1 to 1.5.5.1 and all have the same error message:
http://www.virante.org/seo-tools/duplic ... ent?domain

This site is suppose to be really good as far as a seo audit tool and finding duplication.

This is the error message below I am getting on my sites for every url I test except for the home page where I have done 301 redirections for non www to www . I don't know how to write the code to do redirects for the whole site, well actually I have gotten that code from apache.com but for whatever reason it is not working, my host sd, opencart not built for it?
So who is right ?

Error Message:
WWW/NonWWW Header Check: FAILED
Your site is not returning a 301 redirect from www to non-www or vice versa. This means that Google may cache both versions of your site, causing sitewide duplicate content penalties

Also if you search on adding a trailing slash after all product categories & do redirects the so called seo experts sd, that helps your site reduce duplication and boosts your site up in google index.

So I really don't know what to do as far as this subject. I have gotten down all the rest of the seo for opencart but this stuff, everybody has a different opinion.

Plus Google is suppose to roll out Penguin 2.0 today or very soon which will be a lot of fun!