Option A: Drop the skid plate, remove the ducting and clean each piece.
Option B: Run a hose down the ductwork in place, followed by compressed air and time to dry. If you have a fish-tape, you could also run it through and tie it to a cloth, pulling it back through as a swab.
Option B: Run a hose down the ductwork in place, followed by compressed air and time to dry. If you have a fish-tape, you could also run it through and tie it to a cloth, pulling it back through as a swab.