Finally got around to filling it. Filled the corner areas first then started on the barrel. I put quite a bit of scrap steel in with the concrete. Came in at 1055lbs. There's plenty of room left for chains and tools. I put the barrel on a tilt before filling it so when it sits level, the concrete is pitched to the rear for drainage (just in case). I plan on cutting and welding on a hinged top.
That should serve you well. I made a 1,000 lb concrete block that gets floated between 3 tractors. That kind of weight really makes the tractor perform, while making it much safer as well.