Redirect primary domain to subfolder HELP

[Spaddiction]

I've searched for this in the forums, but didn't find a solution that worked.

I'm on a Baby hosting plan and want to host multiple domains on this space:
primarydomain.com
domain2.com
domain3.com

Rather than have my primary domain served from the /public_html/ folder, I want it to be served from this folder: /public_html/primarydomain.com/

And similarly, I want the other add-on domain to be served from their own sub folders:
/public_html/primarydomain.com/
/public_html/domain2.com/
/public_html/domain3.com/

I'm trying to do this using the .htaccess file in /public_html/, and here is what I've tried so far:

Method 1:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^(www.)?spaddiction.ca$
RewriteRule ^(/)?$ spaddiction.ca [L]

Straightforward, but the problem is that after redirecting, the URL reads:
http://www.primarydomain.com/primarydomain.com/
Of course, I want it to read:
http://www.primarydomain.com/

Method 2:

RewriteEngine on
RewriteCond %{HTTP_HOST} ^(www.)?primarydomain.com$

RewriteCond %{REQUEST_URI} !^/primarydomain.com/

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d

RewriteRule ^(.*)$ /primarydomain.com/$1

RewriteCond %{HTTP_HOST} ^(www.)?primarydomain.com$
RewriteRule ^(/)?$ primarydomain.com/index.htm [L]

This is getting closer, but it doesn't work. Using this .htaccess, http://primarydomain.com redirects and serves index.htm from the /public_html/primarydomain.com/ folder, and the subfolder name is hidden in the URL, but nothing else is served: no images, no other .htm files, etc.

If I access the site using the IP address and the sub-folder, everything displays fine:
E.g.
http://<server-ip-address>/~username/primarydomain.com/

Any ideas on how to modify the .htaccess to fix these problems?

[Spaddiction]

Sorry, my examples were mixed up. Wherever I wrote spaddiction.ca I meant to write primarydomain.com

[Anatol]

In your code for method 2 replace % with %
Anatol