My way around this was to contact the local Consulate of the country to be visited, writing a letter on company paper listing the purpose of the visit and the items of equipment, making a declaration of the intent to re-export everything on departure, adding my VAT number, passport number, all the checkable stuff I could think of to legitimise myself, and then having the Consulate stramp it with official stamps. Some countries love that - looks cool. I was also able to have a second letter from the same people requesting my film bag be subjected to a hand search instead of X-Ray.
It never failed me, and worked just as well at customs on return home. But, it took an X-Ray disaster at Palma de Mallorca to make me do this! Kodachrome and X-Ray mate to make green-tinted tan.
Rob C