Why not get a set of springs made for your van and its current weights. I had Deaver Spring (other spring builders also exist) build a set of custom rear leafs with my loaded and unloaded axle weight specs and desired lift. Being a 4X4 the original springs would have used a lift block, the custom springs eliminate this. If you have properly specced springs, no need for airbags. Yes, custom springs cost more but you save the expense and hassle of airbags. Any good spring builder can get you set up with what will work best for your personal situation.
If you are using your van as a work horse and have a wide range of loads with extreme towing needs, then airbags are very useful. Most or our camper vans do not fall into this category.
Having worked in and around the 4x4 van industry for many years, I have driven way too many vans with all sorts of configurations in suspension and load weights.
2001 Van Haus E350 EB 7.3L Quadvan 4X4
1999 Sportsmobile E150 - SOLD
2002 Sportsmobile RB50 7.3L 4X4 - SOLD