This is simultaneously awesome, nutty, and a bit confusing: A UK-based company called Studio Myfirst has created a flat-pack DIY rotation molding machine called Myfirst RotoMoulder.
The awesome and nutty part is that they made it in the first place and are selling it for roughly US $322; the confusing part is that what you can actually do with it is poorly documented--it's not clear if you can only make the part using the mold they've included, or if you can insert your own molds, and if so, where or how you might make such a mold.
In any case, check out the vid, the first 12 seconds of which you can skip. And the rotation-molding goodness starts around 1:25.
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