IMO the intake should be constructed of stainless or aluminum only.
Mild steel will rust with condensation and will allow flakes and dust to come off before the compressor. This obv has the effect of allowing your enging to ingest rust but also will adhere to the compressor blades causing the efficiency to go down and an inherent imbalance which over time can do damage to the turbo.
www.vibrantperformance.com carries a bunch of options and you get alot for your money.