This may not apply to your situation, but here goes...

I have removed my stock airbox and replaced it with a NAPA 6637 filter and four-inch exhaust elbow. This all connects to the stock intake tube connected to the turbo.

This set up sits behind the driver-side battery. The top of the filter presses against the fender, preventing the filter from moving around. This upgrade gave me a 0.5 MPG increase. I now average 17.25 MPG on a regular basis unloaded.

I guess what I'm suggesting to you is, spend some time at the local parts stores or salvage yards. Look around and see what's there. Inspiration is only a blink away.

Good luck.