you know, lot's of people toss away broken down freezers or fridges.
those can make for pretty good burial vaults.
of course the outside metal will rust, in a few years, but there are "plastic" liners in those things, that will not rust.
the rubber seals around the doors will deteriorate in time as well, but a few "wrappings around with a sealant type of tape, should keep out the moisture still.
another great burial vault, IS a burial vault, made of concrete, and the lid has a seal, that once closed, you need a prybar or jack hammer to break open.
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