These kind of spiders don't use webs your garage can be the cleanest one in Melbourne, all it takes is for that spider to wander in your garage crawl up your wheel and now its a new moving home. Now It can find warmth constant shelter and an endless supply of bugs stuck in your grille, or bugs landing on your shiny fresh washed car at night.
They only come out at night so ill suggest a solution, Get raid or something and spray under the body in all your door jams boot and under the bonnet under the wheels go nuts! And it wont be able to handle it and you should be fine.