If you have done any research into the grey world of an IVA certificate for fifth wheels you'll have realised there seems to be little in the way of clear, easy to understand information.
The simplest answer we can offer to
'does it pass IVA?' is the below image.
Ultralight Rockwood's are UK truck towable and each can acquire an Individual Vehicle Approval certificate from VOSA.
We do provide a service
that will take care of this for you, please ask for details.