Pins aren’t shipped in a heated truck when new, they come on a semi or single unit box truck neither are heated. Another thing, wood expands and contracts mainly due to changes in humidity, changes in temperature do not have a significant effect on wood movement. But that movement is seen predominantly in solid wood, one of plywood’s main benefits is that it is relatively dimensionally stable. This stability is due to how it’s made, multiple veneers that are glued together with the grain alternating 90 degrees on every ply. I’d only worry about it getting wet in an open bed, I wouldn’t be concerned about it getting cold.