Here is all you need in my opinion. All the expertise I can claim is a 2 semester physics class in college, but this is not very complex. Points of contact are what you need to worry about, therefore do not have any legs touching that concrete. Simply buy a solid core door and lay it down where the tank goes. Stain it to match your stand. Place your stand on top of it. That is all you will need. It is cheap and easy and spreads the weight evenly over the area. It also can stick out a few inches depending on the size of door.