At about 14:37 EDT, the landing gear of a Piper PA- 24-250 Comanche collapsed on landing rollout at Naples Municipal Airport. No one was injured. The pilot said she completed the prelanding check and lowered the landing gear about five miles from the airport. She did not see a green light and recycled the landing gear several times with negative results. She contacted Naples tower and asked if they could see the landing gear. She was informed that a medical evacuation aircraft was close by. The medical evacuation pilot informed her that the landing gear appeared to be down. The tower also informed her that the landing gear appeared to be down on short final. A manual gear extension was not attempted based on the medical evacuation pilot and tower reports, even though she had an unsafe landing gear condition. The airplane touched down smoothly but the gear collapsed on rollout.