Looks like 30psi ought to be plenty good for towing

After all this discussion and tangential information, the simple answer is, you can go to maximum pressure as listed on the tire sidewall.

I would personally only do that if I felt some deficiency in the handling of the vehicle, or evidence of underinflation on the tires themselves.

Being a little overweight should not concern you, maybe a couple hundred pounds. Not a big deal, as long as you're under the tire weight ratings.