Years ago I used to have a client in the advertising/marketing agency I ran that had one of these ozone treatment businesses. In the course of developing their sales collateral I learned a lot about the process and we even had him demonstrate it for us in our building and a car owned by the agency owner, who was a smoker.
In a nutshell, I learned that the treatment really does work. It kills mold spores and eliminates odors, even heavy cigarette odors. However, I don't recommend using it in a vehicle as the ozone, even in the small concentration used in these treatments, will damage and age rubber components like seals, gaskets, hoses, o-rings, etc.
Make of that what you will. Maybe not as much of an issue in a trailer, and if you only do it once, it might be a non-issue. But if you use this treatment and find something made out of rubber falling apart a few years down the road, you'll know why.