Hello Bob,
I understand your concerns, and I agree that 51psi seems high for T/A, but generally speaking the manufactures will have checked their documentation for errors, but as we know they can get through sometimes.
If you have the incorrect tyre pressures, you vehicle is technically not roadworthy. As this has both safety and legal implications, I would have thought that the obvious place to enquire about the tyre pressures would be the caravan dealer or the manufacture.
It is unwise to rely on a third party forum for such details as they can easily be incorrect. although some caravans may appear to be similar, there could be some difference that affects the required tyre pressures