c. Where open spaces exist between the different panels which constitute the wall, the floor and the roof of the container, the interior panel shall be fixed, full and continuous. It shall be made in such a way that it cannot be dismantled without visible traces being left behind. d. All containers shall have a placard on the exterior for affixing the agreement certificate. 7. STRUCTURE OF CONTAINERS a. The walls, floors and roof of containers shall be made of plates, planks or panelling which are sufficiently resistant, of appropriate thickness and soldered, clinched, bolted or assembled in such a way that there shall be no interstice which could allow access to the content. These panelling units shall fit into each other perfectly and shall be fixed in such a way as to make it impossible to displace or remove any of them without leaving visible traces as damaging the customs seals. b. Openings intended for ventilation or evacuation may be allowed provided they do not give direct access to the interior of the container. 8. LOCKING DEVICE a. Doors shall be constructed in such a way as to cover all interstice and to ensure that closing is complete and effective. b. Doors and all other closing appliances shall be made in such a way that sealing by customs authorities may be done easily and effectively. c. Adequate protection shall be provided for customs seals and the container shall be constructed in such a way that customs seals are given sufficient protection. 9. a) The conditions laid down above shall also apply to insulated vans, refrigerated vans, and trailer containers to the extent that they are compatible with the technical characteristics that the purpose for these containers impose. b. Compartments containing compressors, fuel and other sources of energy necessary for cooling shall be exempted from sealing formalities. 10. COLLAPSIBLE AND DETACHABLE CONTAINERS Collapsible and detachable containers shall be subject to the same requirements as non-collapsible and non-detachable containers provided their folding and dismantling systems permit sealing the Customs Authorities and on condition that no section of these containers may be removed without seals broken in the process. 11. WEIGHT AND SIZE OF CONTAINERS The weight and sizes of containers authorised for Inter-States Transit may not exceed the weight and the maximum sizes stipulated for vehicles described in the Inter-State Road Transport Convention. 12. PROCEDURE RELATING TO THE APPROVAL OF ROAD VEHICLES AND CONTAINERS The procedure of approval shall be as follows: a. Approval of road vehicles and containers shall be made by the appropriate administration of the country of residence of the proprietor or transporter. b. The agreement shall indicate the date and the serial number of the decision for approval. c. The agreement shall give rise to the issue of an agreement certificate, similar in content with the attached models. These certificates shall be printed in the official languages of the Community and shall be enclosed in transparent sheets made of plastic material and hermetically sealed.