It would seem to me that the added bags would have to be the same size, square inch wise. Otherwise you would have to run different pressures in the bags to insure they are sharing the load.
I know longer have my truck camper, but was on the weight police force at the time. If you are worried that the present airbags are "putting an awful lot of stress on themselves, their mounting brackets & bolts, and the frame where they attach.", you're carrying to much **** weight.
ryoung
I know longer own the TC and truck in my signature.