For my treasure chest cake, I made the lid base from two pieces of cardboard taped together (double thickness). Then, I poked 4 holes through ONE LAYER ONLY of cardboard. I inserted dowels into those holes the right lengths....stuck that down into the cake and bottom cake board... I hope that makes sense, I'm soooo tired right now! Waiting for my husband to get home! LOL!! I'll post a picture.. you can see the dowels poking up...
For my treasure chest cake I used a regular piece of cakeboard trimmed to the size of the cake I used for the lid covered it. I had made a "wedge" of cake on the bottom piece when I was carving it and then it was covered in the fondant at the same time as the rest of the bottom piece. I also had two skewers sticking slightly up more toward the front of the bottom piece for the front of the lid to rest on. All the candy covered that up and since the wedge was covered in the same fondant you couldnt see it at all.
The pic is in my photos. HTH
make it from styro and stick to one side and support with dowels on the other 
http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1493439
For my record player, I also used a cake board covered with fondant & supported it with skewers (painted gold to look like brackets) - it wasnt my best attempt, but I had not discovered CC at the time so I did what I could. I think the Styrofoam would be much better as it's lighter and wont require as much support.
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