Power to shed via extension cord

I have power running to my shed via an extension cord that starts in an outdoor outlet on my house and ends at a power strip in my garage. Note: This extension cord is only plugged in when I am working in the shed. Its always unplugged when not in use. Safety first. I found similar thread below but it is to old to reply to. http://ift.tt/1IUsRMS.

I would like to add an inlet plug like the OP of that thread asked about. One person suggested a Leviton 4937 weatherproof plate. I am trying to located a weatherproof box version of this plug, similar to this box

Does one exist?

Power to shed via extension cord