My recommendation is to have the bags at 5 psi, and measure the height of the rear wheel wells. Then load the camper, start adding air to the bags get so it's 1-2" lower than empty, assuming no level kit.
I think you will find that is a good mix of weight on the bags and weight on the springs.
One thing, don't prefill the bags with a loaded psi, it could easily overinflated them once loaded.
Get the bags at the pressure you want loaded and then record, then you can unload and see what the pressure drops to. That would be your empty pressure.
With my load of about 3K on the rear axle I know that 10 psi empty gets me about 25 loaded and I am good for full weight, 7 psi empty gets me 15 loaded if I don't have a full camping load.