Not hard, I used a hand held air powered reciprocating saw, took it slow and the blade cut through the "reinforcement area'*" pretty easily. I'm sure a small jig saw with a long blade or a dremel with a zip bit could do the same. As well the speaker has a large lip so there is alot of forgiveness when you slide it down in. An audiophile would say you need a sealed box which could be built under it in the trunk. I say the closed trunk IS a sealed box.
Besides, with the dual air compressors, a 3 gallon chrome tank, the air manifold and valving for my air suspension, plus the airlines that feed it all,....I just dont have room for a box. Anyways, I like it, it sounds great, and I like the look. It is not free air, and it still makes a bump nicely with the trunk closed. It'* kind of special when I open the trunk acess hatch.... I tell people thats the "Custom Port"