Yeah I heard about this, but when I do workout back there the trailer is latched open, and I use my pry bar at the top to keep the door from being shut, for the exact reason you mention.
Doctor's Urgent Care which are small walk-in clinics said they do the DOTs for $55. They said best time for walk-in fast service is 8:30AM. That beats making and having to wait for an appointment even if a regular doctors office would be cheaper (which it probably is not).