NT
Just a simple way of putting it with wheels but as you point out rolling stock which is what the carraige is does not come under the RRO
But its not rolling stock Colonel. It's a non mobile structure on wheels used for and by particular persons as weekend accommodation.
Railways Act 1993
Section 83 Interpretation of Rolling Stock
“rolling stock” means any carriage, wagon or other vehicle used on track and includes a locomotive;“station” means any land or other property which consists of premises used as, or for the purposes of, or otherwise in connection with, a railway passenger station or railway passenger terminal (including any approaches, forecourt, cycle store or car park), whether or not the land or other property is, or the premises are, also used for other purposes;
“station licence” means a licence authorising a person to be the operator of a station;
“station services” has the meaning given by section 82 above;
“track” means any land or other property comprising the permanent way of any railway, taken together with the ballast, sleepers and metals laid thereon, whether or not the land or other property is also used for other purposes