Ask the manager or the H&S guru to show you how to safely acess the trailer before you take it out . If they can’t - you don’t (take it out ). If they insist make them put it in writing that you have not been shown a safe method of work for the type of trailer your pulling and refuse to get into it at the other depots . The load may well be rejected or refused so take it back - quickest way to solve a problem like that.