I bought a tank from a buddy who had disassembled it because the seals were starting to fail. He gave up and bought another one on Craigslist and I bought this one from him completely disassembled already. It still took me a year just to get the tank reassembled and ready for a leak test. One of the major problems I ran into is that marineland changes their tank dimensions by a quarter inch every now and then. The marineland brace I bought (this is a marineland tank btw) was 1/4 inch too short on the short length. They didn't even make the correct size frame anymore. I debated for a month on what to do. Here are the options I found. Find a local plastic shop that could custom mold a frame, build a frame from wood, or cut the frame I had bought. I went for option three and cut my frame. I siliconed the bejeezus out of the sucker and filled in the 1/4 inch gap with silicone as well. Then I leak tested the thing for a month in my garage and marked the edges of the gap with a dry erase marker on the glass to see if it was spreading. After a month with no spreading I felt safe enough having it in my living room. I still leave it marked to this day so I can catch any spreading and hopefully drain the tank before I have a flood. Here are the caveats. Mine is only a 120 tall, so you have twice the water to worry about. Mine is also only 2x4 so the lengths are shorter.
This is definitely a try at your own risk, ymmv, please don't sue me for helping you kinda project though. Just because it worked for me doesn't necessarily mean you want have problems.