Counter weight for added back storage area/deck

Sounds really odd. Do you have photos?

Was the hidden storage compartment at the front or the back? I'm presuming that it was in the front. Was the storage area an add on, or was did it come that way from the factory?

Can you contact the previous owner and find out why he had 600 pounds of cement on board?

Maybe it's not cement, maybe it's white powder from south of the border. Or maybe the bags are full of cash!