Hi.
What I think you're getting at is there could be multiple causes or factors to the truck listing. I'll try to enumerate potential causes and effects or remedies as I'd look at it.
1. Front and back lower on 1 side, or just rear? Be on flat levelish surface. Equal air or no air in the bags, measure wheel well to top or center of tire/wheel. This will give you accurate measurement.
2. Does truck list without camper? It's not a newer truck, could be old suspension, sagging spring or 2, front or back. Do the same with empty truck to determine it's the camper causing it. Camper could exaggerate it if truck already a little saggy.
3. Is it the truck, or the camper sagging? Sounds not likely the camper. New camper, equal spacers under it. I would spread the load more than just a couple boards though (separate from figuring out the sagging.)
4. Sounds like airbags were leaking down. With that fixed, can eliminate that.
5. It's 100% plausible that the camper is heavier on one side AND/OR truck is softer spring rate on one side, one corner. It's also 100% acceptable to adjust the pressure side to side to side to level it out. It shouldn't take much difference, 5-10psi, or I'd look elsewhere for the problem. I regularly run different pressures side to side if I'm airing up at home and catch it. OR if the camper is heavier, maybe can offset load it by a couple inches. I do or have done both. No guarantee camper weight is centered in the middle of the camper.
Hope this helps
