was the double // intentional?
Yes as it was for server define

Code:
  define('HTTP_SERVER', 'http://addon domain.com');
  define('HTTPS_SERVER', 'https://addon domain.com');
DIR_WS_CATALOG should be /home/accountname/public_html/topdomain/addon domain ?
NO
Read the comment above that entry
If at the root of the addon
// these paths are relative to top of your webspace ...
(ie: under the public_html or httpdocs folder)
define('DIR_WS_CATALOG', '/');
Your DIR_FS_CATALOG look correct

Actually re-readin you look good

But there is still something amis as you posted ths
/home/accountname/public_html/domainSHOP.com/domainSHOP.com
You might need to post the actual error message instead of being secretive with it
You can use the code <> tags