You can still buy Agfa camera film years after they stopped manufacture. They stored their uncut rolls at -10 C. I would assume that Agfa had studied long term storage and arriived at this temperature as optimal.
Other factors are beta, gamma and cosmic radiation. An inch or so for beta radiation and several inches of lead to reduce any gamma radiation. You would need to store film in a deep salt mine to reduce cosmic rays.
BTW, the Kelvin scale does not go lower than 0oK which is absolute zero so a temperature of -77oK is noonsensical. Whether a symbol is capitalized or not is important in science. A capital K is used for Kelvin temperature.