Two Foxline books by Andrew McRae cover camping coaches across the British Isles, which might shed some light.
As an aside, I helped burn the ones at Abergele in 1971-2 and purchased a complete LNWR door for £1.00. It was too heavy to take home so I removed the droplight/roller/strap attachments plus grab and commode handles and door louver and fitted to them to my workshop. Still got the 'L' handle. The workmen presented me with a Mansell wheel (I think it was off the solitary cove roof coach), which I declined!
LG
Camping Coaches on freight only lines
Moderators: 52D, Tom F, Rlangham, Atlantic 3279, Blink Bonny, Saint Johnstoun, richard