They start sagging pretty quickly, I've even seen brand new ones with the roof already dropping! I have seen frames built on the outside like a perimeter shell, that makes it easier to stack them without making the problem worse. I have seen a build online somewhere that had an inner frame built in it. I think they used 1/2x1/2 square tubing and they did a really good job. The only problem was the welded joints had sharp spots that were a pain to grind down and the welding actually melted the tank in a couple spots. Again, I ask, for price of the tank, why should I have to! I tried a 2x4 in the middle of mine at one time. It helped, sort of. It made a peak in the middle of the tank! If it's not going to be a visual problem for you, it's not a problem, but like I said, if you want it pretty its not good!