You can cut and drill into the passenger side of the wall. BUT... be aware of what you are cutting... a major structural member of the car.

True, the fuel tank is located behind the double wall. The tank also has a titanium plate covering it for safety.

The speakers located in the wall behind the seats are kind of small, so check your depth before you decide to enlarge the openings for bigger speakers.

Look and measure twice BEFORE you cut or drill... Good luck!