Where would I buy a cargo trailer that converts into a stage?

Where can I buy a mobile trailer stage? (or plans for one) I'm talking about the sort of thing you can keep music equip set up and secure. Then you could tow into place, plug in power, raise the doors/sides and have Church or a band perform on. Like a cargo trailer with 2 wings that raise up or 2 fold down wings. I've seen these around, but never up close enough to notice design details. I'd be willing to buy plans or blue prints if I can find a source.Where would I buy a cargo trailer that converts into a stage?
http://www.marshallaustin.com/





Obviously, if you're planning on traveling with the music equipment setup, you might want to button down!