It's not really portable, but it is something I put up and take down as needed in my garage. I made it from 4' x 8' sheets of OSB laid lengthwise across the front, and 4' x 8' OSB stood on end for the sides. All connected with cheap hinges and two pieces of OSB for the top. Initially I used 2 box fans I had lying around but later bought 4 more box fans from Home Depot ($15 each). Added an overhead light and a duplex switch box to control the light and the fans. Also added two panels of rigid foam to the sides to give it more depth. Finally used a couple of the cutouts from the OSB to make a lazy susan turntable to set work on and draped the entry with plastic sheet that I had lying around.