Ive never looked at the plug on a truck camper but why wouldn't the camper be designed to "plug-in" to the line like any other rv? 50 amp service does not use 2 male plugs but typically have a form of plug on both ends. That seems why the extension posted will work. Just thinking this is the example of the female receptacle that looks like a male plug but isn't. Male-male could be dangerous if it has exposed pins and dropped it on the metal truck bed.
Example - this to me :) is a male-female.
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This page:
http://www.etrailer.com/Accessories-and-Parts/Blue-Ox/BX88206.html?feed=npn&gclid=CKu2vfap-rkCFfA7MgodKhEAGgdoes show a yellow female-female but have no idea where it might be used.
This is all new to me. Im just trying to learn.