Has anybody ever seen an enclosure like this?

[Truck Guy99]

I ran across this on the old interweb and was wondering if anybody knew where this came from. I think it's on a square judging by the shape of the cab mounts just in front of the bed that match my square body pickup bed trailer. The enclosure looks homemade but it's incredibly heavy duty and straight. Is this off an older truck than what it's on now? Are they rare? Please help. Is this a good deal at $350 OBO? Here are some pics.