I have worked on a few motors with intercoolers underside of the car. One being an old audi long wheel base quattro which had a couple of coolers (Oil and air) underside. The others ACT is normally ok but has issues with objects hitting the cooler like stones etc. The other problem was getting the air to go through the cooler instead of round it. Had to make a few alloy ducts to channel the air to the cooler. Was a lot of effect and in the end was moved back to the front of the car as they work so well there.