I've actually done this experiment. Moving 300 Lbs from the bed of the truck to the rear of a 5 wheel doesn't changed the total weight, obviously. What it does do is add 300 lbs. to the axle weight of the trailer. On mine it added about 100 each to rear axles, 50 each to the front axles. On the pin weight it dropped about 25. So I kept the tool box in the truck. Did it change the handling? Not really. I haul a 20K trailer, pin weight 4500 so no it didn't make muck difference, just changed my mind and wanted the tools with the truck.