Ok have done homework on rear suspension for towing. Dont use airbags in springs. The spring mounts are weak enough anyway and when you put airbags in springs they are solid and wil break your spring mounts. There are sveral air bag manufactures that make bags that replace bump stops so you have a 2.5 tonn load carry between chassis and diff. Just put enough air in to help support your stock springs and get best of both worlds.