Bil, I made the puzzle photo a bit vague, as it would have been too easy to guess what it was for. I can say it would be slightly larger than a standard size water bag.
My father had a canvas water bag that he used on the front bumper of his TK Bedford truck, when he was out working for the day. They must have been common once, but not many around now. About 6 months ago, on the local Australian eBay, a canvas water bag sold for around $6-800 mark, from memory, something ridiculous like that. I suppose it was a bit of nostalgia, and I don't know where else you'd go to find another.