According to the pilot, during the takeoff roll, a vehicle entered the runway and he immediately pulled back on the yoke in order to climb and avoid the vehicle. The pilot reported that as the airplane began to rotate, he simultaneously retracted the landing gear, and he felt a "bump" before the airplane lifted off of the runway. The airplane ascended over the incursion vehicle and the pilot avoided a collision. The pilot reported that during the post-flight inspection he checked the landing gear to inspect for damage and he did not find any deficiencies. However, during a subsequent preflight inspection by another crew, it was noticed that the lower aft fuselage was damaged. The airplane sustained substantial damage to the bottom aft fuselage longerons and stringers. The pilot reported that there were no mechanical failures or anomalies prior to or during the flight that would have prevented normal operation.