No photo of that particular one but similar in concept to this Alasdair.
The wings were also supported on the slide out section.

What I saw was a metal frame which was the same dimensions as the inside of the trailer,
in this case it was about 7ft x 4ft wide & 4 ft high so quite large.

Attached to the rails running front to back were vertical bars and between these bars were
cross bars with pipe insulation on them to hold wings & fuselages.

At the front & rear of the frame were wheels on legs which telescoped down to support the frame
when it was slid out of the trailer. You could wheel the frame wherever you wanted.

The good thing was you could access it easily from every direction to secure models then slide it into
the trailer, no climbing into the trailer to tie things down. - John.