Really suggest you get weighed, four corners if you can. Many state weigh stations leave the scales ON when they are closed so check that. Often they are built so you can do a 4 corner weighing.
If it were my rig, I'd air those up to 90 PSI and run them at that until you get a good weigh in. Eventually, the tire manufacturer will publish their weight charts like they are suppose to.
Usually you don't go by the RV manufacturers tire pressure label...that is for the brand of tire that was installed and came with the chassis when it was built. And it's often a LOW pressure so you have a comfy ride, but reduced tire life.