Just a thought, but if you are going to cut into your floor, and you have minimal crawl space, why not cut the flooring out under the safe, say 25mm smaller than the safe footprint, then excavate, box and poor a concrete footing with comes up flush with the top of the floor. Boxing can stay in place permanently. Once it is cured, drill and dynabolt the safe down. Would give the chainsaw thief a hell of a fright. For the police, just take photos of the foundations in progress for evidence as once the safe is in place, you would never know that the footing is there.
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