Oh my bad soz. Yeah I vuagely touched on this and agree cold fresh air feed is essential.
Originally I had this intake which was drawing hot air from the engine bay. Heated by the engine an effectively stale air post radiators in my setup...
I spent ages and ages......and ages trying to work out a way of of getting cold to the front of the filter ranging from
**air from the inner wing...but worried about it being really dirty from there.
**Drawing from below the rear valance or even creating an exhaust dummy which would be an inlet.....again concerns of dirty air plus i plan to build a new exhaust extension to exit the stock valance so would interfere.
**I was finally planning to keep the shortest aired option but bending the feed towards the back of the decklid, cutting a hole in the lid and fitting some kind of grill. A shower air vent grill fitted perfect and was blingy chome but decided I just didn't want a hole there as would look a cock and also allow water ingress without a hood (Pope's nose) of some kind. Also looked at decklid options such as the fish gill lids. Unfortunately I couldn't make it easily vent from behind the licence plate as that was my preference. Yours maybe different.
As my setup is pretty unique it's hard to see in this pic. The floors are tubbed and scooped to draw air up from below the car. One side feeds the rad the other the big tube which feeds the intercooler. I extended the air intake accross the engine which was a right pita and is tight as hell bit this now feeds directly from the same fresh air intercooler pipe. I figured it was a small compromise for the intercooler for the sake of clean cool air and it's a big bloody pipe so sure there is volume for both. This doesn't help you much tho soz.
I think your best option is a well designed vent through the face of the decklid.....possibly via a Fish Gill desklid etc or......build a fibreglass box behind the licence plate, drill vent holes and stand-off the licence plate, flexi bend to your inlet (which isn't ideal as dangles in the way when open the lid unless right at the top edge) or a pipe which closes into a seal on the decklid. Toyed with this but never finished it as changed plans. Was going to use 2 slightly different sizes of silicone pipe but you have to be accurate and it's a pain to mark out so an easier job with 2 and if you can get you hand to the engine bay from below.
It's all fiddly and a pain. Seen a couplease of people just cut a hole in decklid for a cone filter to stick through but imho looked a cock!