Old pennies last a long time in the ground.  When found with a metal
detector, lots of them look like when they were lost.  The new zinc ones
turn into an unrecognizable blob in a couple of years.

Steve

For what it is worth, I saw an older single wide home with pull out that
 was a mess inside the owner died and the unit became the property of
the park owner.
To make a long story short they just cut it up and threw the whole thing
 away due to it not being worth it to take the aluminum to the scrap
yard. The steel frame and copper plumbing were another story. Those went
for scrap.

Ed