Napier Outdoors is a very well known brand that produces affordable but at the same time durable and excellent tents. Not only, but they have a line of truck tents that will suit any pick-up truck owner. 

Their models, for example, the Backroadz, will fit right into the trunk of any pick up truck, and can be set up in less than 10 minutes. That way, you can have almost the same comfort of a roof top tent, with the difference that you are set up in the back of your car, and you don't have to carry a such a heavy item and big packaging. These tents are compact when folded, and very lightweight.