I built a stand for my 120, I have some photos of it when it was being built.
I added cross member supports across the top that were attached with joist hangers. These are not shown in the photos. Also the end 2x4's were attached with deck screws (all weather), and I also added small "L" brackets for the end 2x4's that went underneath them.
I used (8) 4x4's notched for the 2x4's. You can see how I notched created the joints in one of the photos.
You can skin the tank stand with whatever you like (barn wood, etc.). I used 1/4" plywood to skin and that way you can add whatever you want over that or just paint. You can add doors into the front also.
All of the tank stand plans I had found on the net, seemed flawed. So I designed my own.
Here are some photos:
Stand
Stand
Stand
Stand
I used 3/4" plywood on the top that the tank sat on.
With my design you may not be able to have holes drilled out the bottom on the very corners however. As the 4x4 corner posts may be in the way.