I believe making a landing page an email won't be as simple as copy paste.
1. The landing page tempalte has a different html content that an email. An email won't render all the CSS styling, it won't accept javascript (which marketo landing pageas uses a lot), and the editing areas are tagged differently.
2. Email templates can be done so they look the same, or at least very similar, to a landing page. You really need to work with a developer that understad how HTML emails work and how the show in Ms. Outlook vs. Gmail for example.
Good luck