Many times some people point to regulations for tire inflation and point out that RV companies select the tire inflation and that is what we should run because they think that is the "optimum" inflation.
Well the reality is that the "Load & Inflation" tables actually are giving you the MINIMUM inflation needed to support the stated load.
First we need to remember that the the load is not your estimate or the load your Brother-in-law has in his RV but the actual measured load that you can only learn by getting on a truck scale.
Here is a comment on tire load capacity.
"Ya might have a valid point if the discussion were about OEM tires.
However this discussion is about new tires on an existing TT. The owner
should go through the process that the TT manufacturer did when
determining tire pressures. Tire pressures should be set based upon the
tires and their actual loads.
Unfortunately, TT manufacturers don’t have actual load information, so they base pressures on max load. The TT owner has (or should get) information that the manufacturer does not have: actual load. That information should be used to determine optimal inflation pressures."