Factual error: They're handling the box/coffin in the warehouse. Eph says it's 2.7m (9 ft) tall and from the looks it has about 1x1m base. So volume is around 2.7 cubic meters. The coffin is filled with soil which has density of ~1200 kg/m3. So in real life the coffin with its contents would weigh around 3200 kg or 3.2 metric tons, making it impossible to handle by hand. The wooden coffin would also break very easily if tried to lift with that amount of soil in it. The antique hinges, and that lone latch on the inside, are the obvious weak points of the construction and would break/give in on the real life. Also later on the episode when "the box" goes missing Eph is mentioning it weighs only 500 lbs (~225 kg).