As long as you did not weigh the seperate axles or better even 4 point weighing, you have to do with the GAWR's ( Gross Axle Weight Ratings).
From the tires you need maximum load and pressure needed for that , written on sidewall.
If you then put those data in my RV tire-pressure-calculator , it might even give lower pressure then the 10 lower you want to trie, and 10 would not give the comfort your wanted, so you stripe away the pressure adjusting, and spend money on things you probably dont need.
On the other hand, if for instance the back axle needs that maxloadpressure, wich is not the maximum pressure of the tire,or a bit higher, you damage the tires by riding with that 10 psi lower.
So first do some calculation, and then trust that.
If you rather look in a list and dont want to use my calculator, I also made lists wich give lower loadcapacity for the pressure then the American lists and even lower then the European lists, and takes care the deflection of the tire stays the same as when maximum load and this pressure needed for that on the tire, wich is the goal of all the calculations. But if you look the loads back in the list, first add up to 10% to it before looking back for savety margin, without loosing to much comfort and gripp. I concluded from reactions, that if the real weight is less then 85% of the loadcapacity belonging to the used pressure, discomfort begins by bouncing, but is discussable.
Over 100% gives tire damage at higher speed, but comfort and gripp even get better, so it is tempting to go to lo, when lowering until you reach a good comfort.
Steering will get a bit heaviër when using lower pressure , but gives probably better feeling for you.
Map with my tire-pressure calculatorMap with presssure/loadcapacity-lists saver then the ones you find on internet
