My RV had sat for 6 or 7 years in a tow yard, leaking the whole time. The interior upholstery and carpet was black with mold and mildew. I couldn't breathe in there, nor could my asthmatic daughter. After steam cleaning the inside, I sprayed the whole thing down with Microban. Several times. Microban is about $40 a gallon and it's the stuff hospitals use to clean up. Mildewcide, bactericide and fungicide. There's no hint of the mold or mildew other than the remaining stains in the ceiling (which are conveniently hidden in the overhead cabinets. After several trips in it, and with it closed up and the A/C on, the kids and I are fine in there.
I also used the stuff in restoring a flood-totaled Cadillac that I reconstructed. It was completely submerged. There was mold and mildew everywhere (if you can imagine muddy river water sitting between the leather and foam on the seats, in the foam carpet insulation, etc.). When I was done it smelled like a new car inside (Cadillac selects and tans their leather to get a particular aroma - another long story).