Clear back in 2002, Family Guy aired an episode (Season 3, Episode 18) that involved a naturist family, and Peter and Lois jump right in ... eventually.
In the episode, Peter saves a drowning man while out fishing on his boat. The Griffins are invited over to share dinner with his family. Lois and Peter are shocked to discover that the entire family are nudists, but their teen-aged son takes an interest in Meg. After devastating Meg with their refusal to accept the "alternative lifestyle," Peter and Lois invite the son to play board games, and shed their clothes to make him feel more welcome.
The episode is available on Hulu+.