I think you are going the wrong way with the van's tyre pressure, but as long as you want to start somewhere start there.Fred K
I will try your / Collyn's theory out on Sat we have a 440K run up to Kurramine Beach.
Just lowerd the pressure of the front tyres on the van to 37 psi with rears at 40 psi and will try small adjustments up or down after that.
Will then try altering the Touareg pressures on the run after that.
It is a very different experience towing a caravan after years with the 5th wheeler.
Seeing you spent such a long time on the road you must know that you must also track the increse in tyre pressure due to heat generated in the tyre which is more important than the actual pressure in the tyres, of course speed comes into the equasion as well, the quicker you go the higher the temp will go.
In my book the best way to ascertain the pressure by load carried is to try to achieve increse to pressure as per the "4psi rule" wherein the pressure differential between cold and hot tyre temperature goes up by 4-5psi, irrespective of actual pressure in the tyres, this is very easy when you have a TPMS on the trailer giving you real time information.