One of my winter's projects included building a rack for my six tanks. I used 3/4 plywood and 3/8 threaded rods (bought the 6 footers and cut the size needed). Washers and bolts rounded out the hardware needed. Found that 4 rods on the bottom section and six on the top section provided enough strength/stability although I still put a flange piece of metal on the ends of the bottom section in each corner to help guide/hold the top on it. Added some rubber weather stripping on the curve cut outs. The result is wicked light, yet sturdy. This was for storage in my garage or basement during off season but I even tried out the rack in the back of my truck and the trunk of my car and it worked well for hauling them around. Here are some pictures.