I actually did this Saturday but just came back from a short road trip to Williamsburg so the kids could have some fun this weekend. I wanted to try a cheap DIY cold air intake and I have only used a flexible dryer hose but I have a spare airbox cover laying around so I chopped it up some, enlarging the cavity around the filter element and opening a larger round hole in the front.
I simply snaked a flexible dryer hose down to where the bumper meets the grill at the non-Rolls Royce spec body gap.
I crushed the opening of the hose to elongate the opening somewhat to grab as much air as possible.
Just messing around with it right now but at highway speeds my IAT is only 4 deg higher than ambient. Going down Saturday I didn't hit any traffic...128 miles down, 97 at Interstate speeds...70-80 MPH and 30 miles of back roads but 45-55 MPH average, AC off.
The return trip was bad, alot of traffic and I caved a few times and turned on the AC when stopped. Every 5-10 miles I hit traffic for about 5-10 min.
The results were better than expected, I don't know if the direct flow of outside air helped but the mileage was better than I have received on previous road trips.
Granted I understand the fuel gauge is far from a linear response and others even get higher mileage, but again this is better than I have recorded especially with the 4:10 rear and I also have the small tank.
DIC showed 22.3 AVG going down and I ended up with 21.4 at the end. I wish I could have run the whole tank out with no traffic but I'm going to try to clean it up a little and see what happens. DIC is taken with a grain of salt and I generally net .5-1MPG difference in real world calculations to the bad side.