There is no right answer, every application is different. You should keep a minimum of 5psi at all times then air up when towing to what feels best. I used 15-20psi on my Tundra with 1k tongue weight.
On a side note, have you actually weighed your tongue? 380lbs is nowhere near enough tongue weight for a 4900lbs trailer. If you're adding airbags because of stability issues I would start by getting the proper tongue weights first. A stable trailer will have 12-15 percent of its weight on the tongue. You should have 600lbs on the tongue at minimum if your trailer weight is accurate.
