This is a strange effect.
Use a Militarytrailer01.mdl from the zone - Military trailers workshop.
Set up the following, Mass 1.0, shape Polymesh, collision type Prop, Physics Mode Rigid body, and hit Fit Shape. then using the FPS Player step inside it and press E near a wall. Then try to move around, inside without falling trough the floor or walls.
You can try on water, or set some CSGs below the Trailer.
Its like your trying to carry the trailer while stood inside it. Can feel like your being flung around the inside of the trailer.