[BiggarView]

Depending on the IS you get it could add 300-900 lbs (if you also level your trailer). Some will argue this is unsprung weight and does not affect your CCC, however scales cannot differentiate between sprung and unsprung weight... they simply read the entire weight so in theory the IS suspension will take away from your CCC since your GVWR has not changed. If you only RV with a light load out, this may not affect your plans, fully loaded out for fulltiming could be a different story especially if something "happens" and the authorities, your insurance company or the courts get involved. Caveat emptor and plan accordingly. JMHO.

One reason for getting IS is you get a true carrying capacity at each wheel carried separately from the other wheels, leaf springs "transmit" acceleration forces/loads to other wheels on the same axle. IS does not. Ride quality is much improved. The leaf spring axle rating is a bit of a misnomer, as axles can be overloaded on one side and not the other and still be under the total axle weight rating. This would be a valid reason for upping a standard leaf spring suspension of say 7k to an IS setup with 8k axles(4k at each wheel) to keep a potential overloaded 7k axle wheel position from being overloaded using a more capable IS rated arrangement. In theory you still cannot carry more than what is placarded on your rig or exceed your trailer GVWR.