Basically your answer lies with the fitting of the PVC cladding ! If this is fitted correctly and properly sealed at the joints, OSB will be fine. If the PVC is not correct, there will be an ingress of water which will be trapped between PVC and sheeting and won't be able to dry away. If this were to be the case, it wouldn't matter what sheeting you used, they'll all rot over time, and in between times you'll have the inherant damp problems. OMO.