How can I make a single post Full Width?

Hi,

I tried several things in order to make a single post full width (without columns).

I even tried the following:
It can be done using this plugin : Custom Post Template – install it and activate.
Create a new file in your theme name it fullwidth-post.php
Copy the full width template page code and add to the fullwidth-post.php
On top :Template Name: Full width, no sidebar (what ever name you have there)
change it to :Template Name Posts: Full Width Posts and save the file
Now when you to posts you will see a drop down menu same way as pages

Now when I edit the post, I can choose full width but the post is still only shown in a narrow view. So I assume the width of the single posts is setup in a different PHP file.

Please help! 🙂

Kenny