Jamming into Sigel

Hello yet again!

I've been looking at the posts about getting a spelljammer into Sigel.  I
still don't have the Planescape set (and I may never buy it), but someone
mentioned that Sigel is situated inside a closed dimension that is shaped
like the inside of a doughnut, and that access is only possible through
portals.  Yes?

If that's the case, then getting a spelljammer in there should be easy!  Just
find or create a portal that can handle a ship.  I know that's overly
simplistic, but if characters can get in and out just by walking through a
portal, why can't a spelljammer get in and out by flying through a portal?

Here's an interesting idea: (Humor me, this is a fresh, untested idea.)

What if some race, like the Juna, constructed special portal devices
specifically for this purpose?  The Juna would have used spelljamming for
most of their prime material plane travel, because there are some points on
the prime plane that can't be accessed through a planer portal.  I admit
that's a bold statement, but it stands to reason that since magic can change
from one sphere to another, it makes sence that in certain crystal spheres,
planer travel isn't possible, or as in the case of Clusterspace, VERY
dangerous.

Anyway, what is the Juna set up portals, perhaps by constructing a magical
"terminal," that allowed an average sized jammer to go through the portal and
into Sigel?  (I'm picturing something that looks like a large version of the
time portal from the original Star Trek series) From there the 'jammer would
go through another portal to wherever it needs to go.  In effect the Juna
might have used Sigel (or what is now Sigel) as a transfer point during
inter-planer travel.

The gates themselves could be controlled by the travelers, or by some kind of
gatekeeper, depending on how devious a GM you are.  These Juna made portals
should be very rare; most of them have either been destroyed or fallen into
disrepair.  Finding one might be an interesting basis for a campaign.

A good place to put one would be in Lostspace.  Lostspace is one of the
spheres in the Vodani cluster that is basically abandoned, but full of old
relics of a past civilization.  It's entirely possible that a Sigelgate (?)
is in there someplace.  Perhaps the Vodani spent a lot of energy and
resources trying (unsuccessfully) to find it?

OK, I've blabbed enough.  Anyone want to comment on the idea of a Sigelgate?

Rich