The 12,044-hour commercial pilot reported that he was flying his single-engine agricultural airplane approximately 300-feet above ground level when he smelled "hot wiring." He then saw smoke in the cockpit and visually observed flames underneath the trailing edge of the right wing. The pilot made a precautionary landing on a county road, and exited the airplane normally. An FAA inspector examined the airplane. A review of several photographs taken by the inspector revealed that the left wing and fuselage were consumed by fire, and the engine cowling exhibited thermal damage as well. The mid-section of the right wing and tip of the elevator sustained thermal damage. This damage appeared to be heavy sooting, paint blistering, and metal deformation, consistent with an in-flight fire. However, the origin of the in-flight fire could not be determined. The pilot reported to the FAA inspector, who responded to the operator's facility, reported that the airplane's maintenance records were aboard the airplane at the time of the mishap, and according to the pilot, they were destroyed in the fire. The weather at the time of the accident was reported as few clouds, 10 miles visibility, and wind from 310 degrees at 7 knots.