There were two different generations of these style of trailer. The earlier ones had a narrower track and don't have the wheel arch extensions / mudguards; the arches are flush with the body.
Clive, I think my office trailer has rockwool insulation as well, but I couldn't remember and wasn't sure if all box body types had it, so didn't want to say definitively.
Mine is Office, Trailer Mounted, 2 ton 4 wheeled Rubery Owen contract WV5478, code no. 6240-0735, CES P/33918/4. The body is FV605923 (and it's had the first five mod strikes applied!). Can't remember the trailer FV number - 2505?
Keeping in the theme of this thread I'm still looking for front axle brakes for mine - it's all original, as it came straight from MoD, but the brakes had been cannibalised so I've got nothing inside the drums!