Since purchasing, approx how many times have you been thankful for the bagsMy bags have been run empty for years without a problem. I even have them connected to an open bleed valve in the cab that I can hear hiss if I hit a large enough bump.
Regarding the springs, the first step is to confirm that they are providing the desired ride height at the Jeep's normal weight. A 100lbs of additional cargo (as described) should not be causing the rear to sink more than a fraction of an inch.
If the springs are inadequate to begin with, bags are not the immediate solution.