There is approximately 200 lbs. of sand in the box, I had used that BP as my basic guideline for construction but wanted to try it without the baseplate first. Ring dampening was part of my thought process as was the ability to store tools in the sand but lack of a good hardwood stump was probably the biggest reason.
Johannes, I'm not sure what you use for an anvil stand, metal I'm guessing but I think in the U.S. the majority of the anvils are mounted on wood. I don't think my wooden box to be anymore of a fire risk than a stump would be, expecially with all that sand to throw on a fire! I have a fire extingisher mounted near my anvil also.