A dual sided opening roof mount cargo box for a carrying vehicle includes a lid portion releasably hinge-connected at two lateral sides to a bottom portion of the cargo box for alternate pivotation at each of the two lateral sides between open and closed configurations. A spring-biased strut is operatively interposed between the lid portion and the bottom portion of the cargo box and located at an end region of the cargo box. The spring-biased strut includes two arms operatively interconnected for pivotation relative to one another and a biasing spring operatively interposed therebetween. The spring-biased strut is configured to control an assisting force to have a substantially zero magnitude when the lid portion is in the closed configuration.