This is especially true for older vehicles, where tire technology has surpassed what was available at the time of manufacture.

My brother ruined six tires on his motorhome following the recommendations of the data plate. The tires demanded more pressure- he ran them under-inflated and they shed their tread. No fun.

Doug- I'd say the mobile service man will have a good idea of what to do, but in general I'd start with the 'max pressure' as stated on the tire itself, and then knock off a few pounds. For example, if the tire max is 80psi, you'll want to not go under 60psi or so. You might start at 75psi and drop down as you drive, based on how you like the 'feel' of it. Remember that tire pressure should be checked (and compared) when the tire is cold, so you have a standard to base your data on.

Running the tires at the maximum allowable pressure will give you a small contact patch (as already mentioned). This is great for fuel mileage, but horrible for safe control and ride comfort.

Good luck on the move!!
I'm out of town this weekend, but if you still need some help next week be sure to call me.