I have Plesk - How can I do SSL from my httpdocs folder and not have to duplicate everything in httpsdocs?

If you are you using Plesk, then go into your Plesk account profile, click on "Setup" and then enable the two checkboxes which say:

• Enable SSL
• Use a single directory for housing SSL and non-SSL content.

This way your site will be able to serve both SSL and non-SSL from just the httpdocs folder.  The httpsdocs folder will not be needed, since Zen Cart can switch back and forth between modes as necessary.

If you don't do this, you'll have to install two copies of Zen Cart: one for SSL in httpsdocs and the non-SSL main one in httpdocs.