I'm going to try and provide a sorta outline for how I made my base, I have a design made up for a 2x5, but hopefully you will get the idea.
First a picture of how the bottom of the cage was made, to support the future coroplast:
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The base is in there, but hard to tell what it looks like from a side view.
Secondly this is how my supposrt system would have worked if I had of made a 2x5, I used a similar one for my 2x4:
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If you still have trouble I would gladly compute on up for your cage, if you still need an idea.