t roy you could use two 4"x8" beams running parallel to your floor joist then a 4"X6"cross beam under them with support posts under it to the floor or ground . That way you would have one end sitting on the sill plate of the foundation and the other end supported by your posts . adjust your beams under your safe so you can bolt through them for extra security . If the posts will be sitting on soil you will need to put a pad under them and use wolmanized post to keep out termites .