At -40 deg C, the CVN impact energy will be below 27 J. I would not risk using this material at this low of a service temperature. You need to upgrade into one of the low temperature steel grades that contain some nickel - like an equivalent to ASTM A333 or ASTM A350 material grades, where specific impact testing is required by the material specification.
You should also make sure you select a suitable welding process and filler metal for fabrication of the trailer. As a minimum requirement, I would recommend you follow a recognized code of construction (like AWS D1.1 or ASME B&PV code) for welding and material procurement.
Heh, heaven forbid that the europeans would deign to use an existing working standard instead of creating their own incompatible one just to be different.
