Oh wow that one was nasty! I had a case one time on my cousins Buick. There was a foul odor coming from the back area and it turned out she forgot the gallon of milk in the trunk. After sitting in there a couple weeks in the August Mississippi heat, the sealed lid popped off. After promptly throwing up and tossing the bag with milk as far across the yard as I could, I had to remove half the padding under the carpet in the trunk. Like you I had to clean the spare tire well. The smell never did 100% go away. She was a heavy smoker and would smoke with the windows up, so Im sure it wasnt noticed after a short time...