Hi, had a question about the return air "box" that my Trane XE 80 sits on. The system is located in my garage along side a water heater. I live in Arizona.(Dusty) The construction of this "box" is OSB ,drywall and a concrete floor. While changing the filter I wondered if this area was a poor design and was allowing dirt/contaminants into my home. My family suffers from allergies and I am constantly keeping filters changed and. ducts cleaned. Should is area be sealed and made of metal or some type of ducting? I was thinking of purchasing one of those Aircycler controllers to use the system to filter the inside air for periods during the day. I am concerned that this plenum could is cleaner and better constructed. Any ideas or input is appreciated.