As previously stated, COPRA (Combined Operations Pay Records & Accounts) = Commissioned as Combined Operations Pay & Drafting Office 30 August 1943.
So unless he was serving at the actual accounting base, "on board Copra" isn't quite correct right.
Anyone with "HMS Copra" on their record was serving with Combined Operations, Landing Craft, etc. COPRA was just where his records and pay were administered.
For more details web search for - combined operations Scotland.