Make sure you do some research or ask questions in the Apache forum to get the proper usage of the [L] qualifier so you don’t end up in infinite redirects.
I can confirm it will NOT degrade your rankings (provided that your redirects are set-up correctly).
What this does in effect is consolidate all your backlinks that those variations have accumulated, so you should (depending on the number/nature of those backlinks) see a net benefit.
As for the .htaccess bit, i am NOT an expert in redirections and regex, but this should work fine:
if you need to force the trailing slash (you must check that doing this won’t break other parts of your site), then you can use the following .htaccess:
Make sure you do some research or ask questions in the Apache forum to get the proper usage of the [L] qualifier so you don’t end up in infinite redirects.