My '64 GMC longbed stepside must have had a leaky battery sitting in it at some point. There was likely some sort of hose explosion too from the surface rust on some of the other parts as well.
I got the battery tray removed, and of course one bolt was seized and had to be reminded who was boss.

There were a couple of nasty pieces of wood under the battery, and the bottom of the tray was nearly eaten all the way through.
I could just buy a new one, but what fun would that be? So I tried my hand at electrolysis rust removal. I used a motorcycle battery charger, and next time I'll put the battery in between the charger and the electrolysis rig for safety.
Anyway here are the pics. As I complete the tray I'll post updates.
http://captaincheeto.com/pictures/64-gmc/batterybox/