If you've done all that tank cleaning it sounds like the air conditioning has become stagnent. I would put some type of strongly fragrant liquid freshener into the tank through the roof vent pipe then see if you could smell it comming from the air conditioning. Using the roof vent would keep from presaturating the inside of the trailer with scent by pouring it down the drains. If the air conditioning still gave off a bad smell and you can't detect the fresener then it could be the air conditioner or vents has something bad growing in it due to excess condensation. I had a 24000 btu window air conditioner from the house that got really stagnent. Had to remove it to wash and scrub the coils and clean the drip pan. It was starting to smell like rotting leaves.