Somehow the van might (but I doubt it personally) be an old fire department truck but my bet is that box came from something else. Maybe it was a fire department box that was totaled and replaced by an accident with a trailer (like the ad says). Someone was giving the box away and someone used wood of all things to mount it to this van that was who knows what in its past live, so it had something on the back to try and sell it. It is kind of cool looking at first glance and if it was really properly mounted and in good shape it could be used for something maybe even a camper van with exterior storage. But as it is its too big of a project for all but a select few...eBay sure has some junk for sale sometimes...
2008 Ford E-350 V-10 EB
U-Joint Off Road 4x4 kit in the garage
2004 F-350 Dana 60