Radio Flyer Trap

Good morning,

             My Wife and I have a 10 mos old son who will be enjoying his first Halloween this year. To take part in the fun we decided to dress up as a family. The plan is for her and I to go as a Ghostbuster and him as Stay Puft. Thats the easy part (We think). I'd also like to convert the linked Radio Flyer Wagon into a ghost trap. This way he can sit back and enjoy the ride while also still taking part in the theme. I've looked online for plans as Im not very good with my hands. If anyone has any plans/instructions for building something simple out of cardboard or thin ply wood, I would greatly appreciate it! Thanks in advance!

Radio Flyer: http://www.toysrus.com/product/index.jsp?productId=2266708