The Pan-American Highway runs the length of southern Peru, some of it along the coast, some through desert, and some over plateaus and mountains. It's paved and in good condition, but be sure to have fully equipped first-aid and repair kits. Besides breakdowns, hazards include potholes, rock slides, sandstorms, and heat. You'll find many service stations along this route, most of which have clean bathrooms and convenience stores. Off the highway, conditions are less predictable. Roads may be poor in the eastern highlands and around the Paracas Reserve. Four-wheel-drive vehicles are recommended for all driving except on the main highway and within major cities.
Your only real options to rent a car are in Lima or Arequipa.