Nobody can tell you the correct tyre pressures for your van. You need to load it FULLY with everything, food, fuel, water, passengers and all. Then take it to a weighbridge to get the individual axle weights. Write then down - you could misremember.
Once you know the axle weights, read the load rating and maximum pressure written on the tyres.
The load rating is the maximum load for that tyre (so double it for the axle) at the maximum pressure writrennon the tyre.
The correct pressure is proportional to load.
For example, if the load rating is 1400kg at 65psi max pressure, and your measured axle weight is 2200kg, the correct pressure is (2200/2) / 1400 x 65 = 51psi.
Under inflation is worse than over inflation, so I suggest adding another 3psi, giving a result in this made-up example of 54psi