Put on the plastic and pay it off asap 

We went to look at it toward the middle of March 2015 and there were holes in walls, missing fixtures, odd electrical (the wiring for the back porch light and exterior outlet have been pulled into the master bedroom), tiles missing in the master shower (green plastic was duck taped across 2/3 of the surround so they could use it anyway), and cabinets missing that were not that way in November when it was listed with our Realtor.

Send the notice by regular first class mail, certified mail and have someone local post it on the door in a conspicuous place (put it up with good heavy tape & protected from rain or covered with plastic) and take a picture of it for your records. 

I have now put a plastic cover on it to stop it from getting wet but those lights need air circulation.

How about a plastic tackle box? 

Most are value engineered to hit a price point with cheaper plastic parts, valves, cartridges.

They also spent their own money on plastic, tape, and paper to cover.

Is there any type of plastic or shield I can install under the new pergo floors and carpet that will lock the un-reomved smell in? 

If the pipes are galvanized and subsequently rusted or deteriorated then you can either tunnel under the house (stupid and unsafe if not done correctly) or hammer the slab and replace it with plastic. 

The family was in the house in full body plastic suits and respirators.