Needed tire-pressure is all to give the tire a deflection for the load on it , so it will not damage by the 10 to 20 times deflecting and flexing back of every segment of the tire.
So if you know weights on tire , I can calculate a lowest save pressure at wich no damage. If you estimate the weights you have to keep to more reserve
When towing you have more weight on rear axle , even if you use a Weight distribution Hich ( WDH).
So you would expect a higher pressure needed to give the tire a save deflection.
But because nowadays pressure advice is given for even higher loads then the 2 tires on the axle are allowed to carry by law ( GAWR= Gross Axle Weight Rating),you maybe end out with a advice of not higher then 35 psi.
35 PSI is the AT-pressure of a P-tire, also called reference-pressure/ maxloadpressure/ pressure needed for the maximum load up to maximum speed of tire or if lower 160 km/99 m/h.
For lower speed ( you will use when towing) the maximum load is higher for the same AT-pressure///.
The AT-pressure is not the maximum pressure of the tire, as they give on P-tires and XL/extraload/reinforced, From C-load ( AT-pr 50 psi in USA system) they give AT-pressure on sidewall and you so are allowed higher then that.
So try to give as much possible data of car and tires, and I will calculate.
Greatings from a Dutch Pigheaded Self-declared tirepressure-specialist