Rowly,
It's a commercial tank for fish hauling and even has gate valve to drain it and is sloped for draining. It's called a Port-A-Pond and is made by a company in Minnesota calle Rotamold. Cost was $1000.00 and I've used it for fish hauling trips up to 13 hours. If anyone wants info I can dig it up.
As far as the earlier comment on the freezer, a chest freezer would have a lower volume and center of gravity than this particular tank. And of course you don't fill up tanks completely anyway. Only question I would have would be if the freezer walls would be strong enough. Many now seem to have plastic inside walls. But if they were strong enough maybe inject foam inbetween the inside and outside walls for insulation?
I've heard where there are big casket manufacturers people have made fish hauling tanks out of them.
