Cleaning out mold is more difficult than most think.
One must rid the camper of all of the mold spores. They get everywhere.
In order to effectively rid the mold spores, you may want to empty the trailer of all it's contents. Wash all of the fabric and dry it thoroughly. Then wipe down every hard surface in the trailer with 10% bleach solution to kill all of the free mold spores in common mold .
The key to keeping mold from maturing is "AIR CIRCULATION". If there is air circulation, mold will not grow. Putting a cover on the camper (breathable or not) will stop air circulation (unless you are in a dry/windy area).
You may want to consider a portable garage type cover for the trailer.
