The lower StableLoad wedges act like a lower overload spring that has been re arched to match the profile of the rest of the spring pack and work well.
In TC applications, you do not want the airbags to be the majority of support for your load due to the higher CG of a camper. This is why it is suggested to preload the existing springs or add additional ones for this purpose.
I also run the Firestone bags without the complexity of a pump. Make sure each side is plumbed separately of the other and it will work well for equalizing and fine tuning your truck attitude.