So,... I have been digging around trying to find examples of people safely burning out fence post stumps from concrete anchors,
You need the barrel to make it smolder. No burn, instead of propping barrel up, cut a slot in barrel and screw window screen over it. The screen will keep hot things in and let air in. Make one and try that baby out. I'd even be soaking the others with diesel so they will be ready to smolder down. Around here stumps are soldered out. But you could cut a hole in bottom of drum too to speed things up, 4x4 or so. Screw screen over hole. Your posts are dry and should go fast. You can twist 5he drum so it cuts into ground and no embers get out. Try one and see if it gets done over a weekend.