Well done Gary. I think your way would have been less effort than mine.
I've had a ballast box fabricated from steel plate and intend to throw lead in it and top it up with cement. Sounds easy in theory, but because half of the lead I've accumulated is roof flashing, I still have to melt it into ingots (made about 300kg so far). Also need to take the box to sand blasting before coating with zinc paint. I don't really have the room in the yard to make a bonfire like yours, my method only needs a gas cylinder, a large size burner and a cast iron pot so I guess thats a consolation...