Aluninum sheeting along with rtv sealant would work fine, close up all the openings, Check the area in front of the engine as this can be a 1" gap that runs full width of the engine compartment , Get under the car and look up in that area, Most cars show this defect. We use high density foam to seal this gap , Also behind the engine the rubber seal is usually destroyed by heat, replace with high temp silicone material,
Intercooler mist systems can be used to restore some efficiency , There are some very good kits out there, As you continue your search for better Intercooling consider a temp. instrument (in/out),
Good luck with your project, Lou / AERO DYNAMICS