Tach, I have seen those cargo shelves, too -- they go into the hitch receiver. And I often see plastic gas cans on them. To me, that looks unsafe -- the gas cans, no matter how well secured, are right at bumper level. Any little bumper thumper will cause the gas to shoot all over the hot engine of the car that just ran into the gas can -- kind of a harsh punishment. ;)
So that is why I have mine far above bumper level. It is much less likely to come loose during a routine rear impact. But a catastrophic impact might destroy the rear wall of the trailer, which is what supports the steel framework of my gas can platform.
