I have just enough to level the truck out.
Instead of trying to eyeball it you can measure from the bottom of the wheel bead up to the highest point on the fender opening. Put a piece of tape there with the height you measured, then load the trailer up and just add air until you get back to that measurement. Remember the psi and you should be good from then on.
Then deflate to around 5 lbs when empty or whatever is comfortable to you without them being completely flat.