Simple, but extremely effective method of
moving a step unit wagon on and off stage.
 

A 2x4 guided via 1x3 screwed to the deck

 

The crew waiting for GO

 

Pushing the wagon

 

Pull the rope DS and pull the 2x4 back in.

 The wagon snugs up against the unit hiding the hole it came out of.

Reverse the step for taking the wagon off.

Thanks to Elizabeth & J.J.