It all depends on van weight, tire size, and tire load rating. There are other threads with the details if you search the forum, but my understanding is that you can calculate your minimum tire pressure using official Tire & Rim tables (https://octopup.org/car/tires
). Which tire manufacturer doesn't seem to matter.
For my van, which is a lighter (<9500 lbs) RB-50, I run 35 front & 50 rear on my D-rated LT305/70 R16 tires, and then air down below that when off-pavement.
This may seem low to some of you, but I did the math after weighing the van on each corner. I do watch the tire wear, and the temperature on my TPMS.