Just drill a small hole to the point where it penetrates only the wall panel. Then take a straightened out paper clip and push it into the wall cavity and feel for items inside the wall. If you feel no resistance you can put in wood screws as far as your paper clip went into the wall. Any electrical wires will not be punctured unless they are forced into something solid inside. If you feel unsure about doing it this way you can use screws that have the points ground off, or if you have some,... use screws without sharp points on the business end.