I've done one based on Hogan's Heroes, of all things. Unpublishable because it's fan fiction and that gets into copyrights and things, but it worked surprisingly well, maybe because there were no "Mary Sue" characters.
Uh, unpublishable in any sense, because the characters are not in public domain. This means fan fic usually violates copyright unless the characters are used by permission of those who hold the copyright. After making a previous post in this topic, I found another fan fic, a short "interview" that is basically an opinion piece but using a well known character set in a well known imaginary world, neither of which is public domain. That, too, will never see the light of day. It was fun to write, but that's about all. There's too much risk involved.
I did a couple of Aetherlight fanfiction stories as well. Basically, I need a good fandom that piques my eccentric interests to do something like that. Except I don't, because I have no time for that these days. All of my time has to go toward money making and ministry. It seems that fanfiction is an amusement of the young and young at heart. It's good novel writing practice.