There have been a couple of other versions of the Cobra spare tire
mount.
Under the nose on the floor works if there is room (vintage 1988) If
the tire is too large you'll need a towel over it so the glider belly
doesn't turn black. As JJ mentions, the fuselage comes out to get to
the spare, but not a headache the one time I used it.
Bolted (upright, across the trailer) to the front of the vertical
tube holding the nose cone (vintage 1999) works too, if there is room
behind the storage bin.
Jim