Exactly how big a garage are we discussing here? And what kind of budget are we looking at? If the latter's no concern, here's how I might do it:
Entering through the workshop is good. As the viewer turns to go into the hole, the theme kicks in, slowly but surely. Down the hole they go, having to duck to avoid that pipe Wembley always manages to smack into, which belches steam. They go a few yards, then veer to the right and find themselves in Gobo's room. He's reading his latest postcard while Wembley nervously glances over his shoulder. If you have any of the soundtrack albums, insert a song relevant to these characters here. Another sharp left, and they break through the wall. Now they're in Red and Mokey's cavern. The former is eagerly bouncing up and down on a trampoline, while the latter paints her doing so. Repeat music theme mentioned before. Outside they go, having to duck again to avoid a maze of Doozer constructions built over the track (perhaps have familiar Doozer characters call out not to ruin these?). A sharp left, and they're now about to run over Boober, laconically going about his daily laundry. If you can do a halfway decent impression of Dave Goelz's Boober voice, perhaps dub in some dialogue of him crying out at this intrusion and asking what the riders want with poor him. They go down another tunnel, the colors start to get a little darker. They pass by Cantus and the Ministrels coming along a side tunnel playing their music and veer sharply to the right. Now comes the "danger" section, with flashing strobes, more steam obscuring the viewers' vision of what's to come, and an uneven track that can unexpectedly drop or spin, depending on what the budget at hand is, perhaps even a trick where the track seems to be coming apart underneath them. You could also throw in a monster or two here (I'm thinking the Invisible Gargoyle might be the most economic) They start picking up speed and shoot for the hole into the Gorg's garden (alternately, you could also have it go out Gobo's tunnel into the castle and go around there a bit). "Take that!" yells Junior, swinging his club at the riders as they emerge. Ma screams and leaps aside as they go by, while Pa comes running out of the castle yelling that the Enemies of the Kingdom stand no chance against the fearsome might of the Gorg Empire, or something similar, whatever you can arrange. Veer to the right, passing the Trash Heap. "Better be careful," she advises, "Wander McMooch is afoot" (or something similar; Philo & Gunge bits?). Things get darker as they go deep into the woods beyond the Garden. "I've got you now!" McMooch is perched on a tree above you. He's about to drop a boulder on you, but just before it hits...the set bursts open, and we're back in the Great Hall, surrounded by hundreds, maybe thousands of Fraggles, with our heroes right at the center by the pond, all singing the main theme merrily as loud as they can, and rest assured no one will resist singing along. Finally, we see Traveling Matt by the wall, as he pushes aside a boulder--probably falling on his face in the process--letting you back to Outer Space.
So, do you think it would work?