As the flight neared the intended destination airport, the pilot entered the traffic pattern for runway 26. The approach was normal; however, the landing gear was not extended prior to touchdown and the airplane inadvertently landed gear up. Damage to the airplane included external structural formers on the bottom of the fuselage. The pilot noted that he had failed to lower the landing gear during the before-landing checklist. There were no failures or malfunctions associated with the airplane prior to the accident, according to the pilot.