Crossovers that MUST be

[Jorlem]

To be honest, I think that using the Garden as a vessel was the original plan in canon. Given that it ripped itself apart across dimensional faults, and then imploded into imaginary space (or something along those lines) when the jump was attempted with insufficient Jewel Seeds, I think its likely that Precia had the place rigged up as a massive dimensional transport from the get go. It was powered by a Lost Logia of the same type as the Jewel Seeds, albeit weaker than the Seeds, after all.

Again, consider that Precia had no idea what condition El Hazard would be in upon her arrival. For all she knew, it could have been rendered permanently uninhabitable by the war that threw it into the dimensional void, or wherever. It would only make sense for her to bring a base/space station, just in case.
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Stand between the Silver Crystal and the Golden Sea.
"Youngsters these days just have no appreciation for the magnificence of the legendary cucumber."  --Krityan Elder, Tales of Vesperia.