Dear Jim,
The following are some references that could merit further research:
Memoirs of the Duchess D'Abrantes Vol VII, London (1835) Note to page 358 states that the arsenal of Saltzburgh contains some specimens of leather cannon.
Napolean of the Other World - A Narrative Written by Himself, London (1827) refers to the first leather cannon employed by the Venetians against the Genoese.
Life of Oliver Cromwell by Rev. M. Rusell LLD, Vol II (1836) refers to "a traine of artillerie of some field-pieces and leather cannon ..."
What we do not know is whether these leather cannon refer to the same type of artefact that we are discussing.
Your Edinburgh reference does recount that the cannon was fired three times without the smallest apparent injury to the leather suggesting that one would normally expect to see some injury to the leather hence fired in the leather chamber and not within a leather covered metal chamber.
Best Regards.