Removed existing return plenums and supply plenum elbow. Built and installed new extended return plenum, increased to full size all the way to the filter. Built and installed new full size supply plenum with elbow, going back to the two trunk lines. Added new supports for the plenums to sit on. Sealed ductwork connections with mastic/hardcast. Cleared primary drain with CO2 and primed trap with water. Tested system operation and static pressure. Everything is working at completion of service.