The pilot landed on runway 20 and taxied toward his T-hangar. Night, visual meteorological conditions prevailed. As the pilot entered a general aviation parking ramp, the right main landing gear struck a parked helicopter dolly. The right gear collapsed, the right wing forward and aft spars were damaged, and a fuel leak resulted. The Federal Aviation Administration inspector and the airport authority reported that the parked dolly was adequately marked. The pilot reported that he did not see the dolly prior to the collision.