A pickup truck cargo box subassembly includes a load floor composed of a sandwich structure having an upper skin, a lower skin and a core extending therebetween. The upper skin is formed of a composite material including continuous reinforcing fibers. The pickup truck cargo box subassembly also includes a left inner sidewall panel having an integrated left inner sidewall panel joining surface extending horizontally along at least a portion of a length of the left inner sidewall panel. The pickup truck cargo box subassembly also includes a right inner sidewall panel having an integral right inner sidewall panel joining surface extending horizontally along at least a portion of a length of the right inner sidewall panel. The left and right inner sidewall panel joining surfaces join a peripheral portion of the load floor. The pickup truck cargo box subassembly also includes a headboard and a rear cross sill.