Perth is a large city where you don't need a vehicle to get around, but if you want to go camping outside Perth, you'll be looking for where to rent a campervan. Some great places to go camping around Perth are in the corner of south-western WA, and along the coast north of Perth.
While backpackers often look for cheap options such as the bright coloured Wicked vans, it's a bit more expensive but much safer to use the large, well-known companies such as Hertz, Maui, Thrifty, Britz, Apollo, Avis and Europcar. With them, you know what you get, you can get a one-way rental, and you get help should you break down. They also have service stations in larger towns where you can get you vehicle checked before you take off to remote places.
NOTE: This website is written in British English, which is the English we use in Australia. You will find words like "traveller", "harbour" and "realise", and they are all correct in the language used in Australia.