Definitely inside. Back in the 60s my father worked the YWG ramp for AC. Called home one night to say "I'll be late". Got in 4AM, had been grilled by RCMP re hash on AC Western Arrow (LHR-YWG-YVR). Actually it was Dad that found it on top of a ceiling panel in a rear loo. Was LHR staff working with ME contacts.
Also in the 80s, packets of blow were found in mx spaces on the wings of A320s working MBJ-YWG. To access these spaces you need a special tool, not just a Robertson screwdriver. So it was obviously not SLF trying to mule something.