The missus and I went out today and put money down on a gun safe. The one we chose tips the scales at just shy of 900lbs empty, probably half a ton loaded. We shopped a few different places, and one of the sales guys mentioned reinforcing standard flooring before installing the safe. What are the best methods for shoring up floors under a safe? Additional joists? Cross bracing the existing joists? Sheet of plywood to distribute the load?