I have never been a fan of having the softener system in the same space as the hvac system. I do understand that having a separate space is not always possible nor feasible. Bottom line is pay attention to the system and do not store the salt in the indoor space. If you do, make sure it is sealed tight. The furnace was newly installed in the fall of 2015 and this corrosion essentially had to start when the a/c came into operation. The softener had failed and was leaking unbeknownst to the owner and as shows many things began to be affected. The condensate drain became clogged with particulate and scale that fell off which created the overflow issue and resulting damage.