Throwing this question in the chit chat area. Has anyone ever converted a reefer trailer? Is it even possible?
Do you mean as a stationary tiny house or a mobile dwelling you would pull behind a truck?
They tend to have good insulation and are built well, but by the time one is affordable in the used market, it has probably seen its better days. There may be cracks in the frame, rust, sheet metal missing, leaking roof, or mold in the insulation...or any number of problems after a few million miles of use. If used for a mobile dwelling, you will need to service, and possibly replace, the running gear (springs, axles, bearings, fasteners, air brakes, etc) and check and repair/replace all the lights as needed.
Of course you will NOT want the refrigeration unit, those things are noisy as hell and expensive to run and maintain. But once it's removed, that will allow you to install a normal window A/C unit in the opening.
And you would need to install windows and doors, vents, etc to make it habitable, assuming you found one that is otherwise safe to occupy. And it will need a new floor and/or carpet over the existing 'wet floor'.