Just go a pod of some form. One of the AVO ones or a K&N Hurricane I think there were called. Honestly, the noise into too bad. I have a 4" inlet turbo and a pod hiding under the battery and you wouldn't know the thing was modified more than an exhaust unless someone pointed it out.
I does make a 'little' noise as at the turbo spins up though.
Try and find a 2nd hand one; worse case you can flip it for what you paid for it.