On the front bonnet I just used foam, about 1" or maybe slightly thicker, glued to the inside edges of the lid. How thick depends on how compressible it is, it's only forming a rough seal for the plenum chamber. I ran for years without any and although it made a difference when stationary, when you're on the move you get plenty of air pushed in.
At the rear I have a small strip at the front of the engine bay, conventional "bulb" seal which goes roughly the width of the window. At the rear I have nothing, when I tried foam on the rear boot box it was more trouble than it was worth.
Brian