I saw this on craigslist as well. I thought the guy said it was homemade, which it looks like. It seems like the round design would make it difficult to fish more than one or two guys out of.
I’ve got one sitting on my flat bed right now. It had embalming fluid in it that reeked. They’re actually for stationary use. Maybe if you could insulate it somehow it would cut out the echo. You ever put a 5 gallon bucket up to your sunflower heater. Think of being inside it.