Bob Clark did make an "official" sequel in the 90's.
It was retitled "My Summer Story" on home video. Obviously all the parts were recast because of the passage of time, but it did have Jean Shepard's narration.
Coincidentally, this nearly forgotten horror gem is finally getting a DVD release in October as well.
I think of it as "Ralphie's Really Scary Desert Vacation". If you've ever seen it, you know what I'm talking about. ;)