AFAIK, having owned one of those finnish glider containers, the "trailer" is a composite box which was used as a cradle for shipping the gliders to their owners.
It was up to them to fit an axle and tongue. So everyone is different when it comes to road-wrthy parts. My container was in facts simply bolted to a low H-frame structure with twin axle made in Italy. It's still doing well.

Aldo Cernezzi
www.voloavela.it