Low oil pressure makes me nervous

FYI
About a month ago I towed our camper with my 360 truck, I seen the oil pressure go down to 40 psi on the interstate 3000 rpms, 5W-30, fresh cut crank, recondition rods, 180 deg f temp on the gauge, stock melling oil pump. Motor rebuilt 2000 miles ago.
I was not worried at all, when it starts cold it 70 psi plus.
Its just the physics involved, hard pull, with alot of weight 3500# camper and 1500# in the truck bed, is going to make heat, and when oil heats up it thins out.