To be quite honest, I don't think there would be any problem leaving hired GA aircrft at Jacksons. Just make sure the doors are locked to prevent the airport security guards from sleeping in them. Up outside the Aero Club would be the safest place. I would also throw the Protect Security guards up by the gate at Pacific Helicopters 100 bucks to keep an eye on the machines. In the 12 years that I have been in PNG I have never seen any aircraft tampered with, as most of the locals use aircraft as public transport to get around the country.