OK, I've woken up and realised that a 13ft trailer cannot have a 12ft body - even the short tongues on commercial trailers aren't that short! What made me realise it was that when I scaled out the height with a 12ft long body there was nearly 7ft of headroom!
So now I'm thinking that an 11ft body is about right and also gives a headroom a little over 6ft with the dropped floor. It fits the photo you took, Woody, as well, once I'd flipped and rotated it.
Your photo is of the left side, which is how come the photo has no door.....
What I believe is the standard 13ft Scotty layout seems to fit into this size:
So I'll start drawing out the geometry of this profile, unless anyone tells me I've still got it wrong. It may take some days, as I'm supposed to be doing something else, but this is a good 'displacement activity'....
Andrew