I like to use 4x4's run through the planer enough to square the corners. I then calculate the pounds per square inch they will be loaded and try to keep that under 30 pounds or so per square inch. I then sheet the top and bottom of the stand in plywood to help spread the load. I generally also have 2x4's running one direction one the bottom and the other direction on top of the legs before using the plywood to help spread the load over more space on the plywood then the plywood also helps spread the tank and floor load over more space. Has worked good for me with up to a 600 gallon plywood tank.