Geometry files do not enclose volumes but only single surfaces

Dear Sirs, I am trying to import the geometries of truck and trailer using Ansys Fluent and Rhinoceros. I am able to open the files and to visualize them, but unfortunately the surfaces do not seem to be connected, therefore I am not able to create a numerical domain. Can you provide the geometries as volumes? Thank you Paolo

PS: If I use them in OpenFOAM there is no issue.