Steve,
Shame you ripped up your previous layout, as it was looking great. However, I understand the urge to go back to China Clay lines. There is a definite attraction for them. One point I will make, and I hope you won't take offence at it. The Skytrex wagons are NOT correct Clayhoods.
Clayhoods, UCV, in TOPS, were 16' overall length, with a 9' wheelbase and have an end opening door. Unfortunately, there is no manufacture of this type in "O" gauge.
The only thing I can say is, if your not that worried about correct diagrams for wagons, then the Skytrex models do look the part.
You could always use Paarkside kit GWR 12 Ton Open Goods Wagon 032/33, which is a good representation of the Clayliner wagons that were just tarpaulin covered, and were used to transport clay to the Midlands and the north. The other one that can be used for this trafic is the Dapol 7F-053-005 5 plank corrugated end BR Diag.44.
Anyway, I look forward to seeing the China Clay line develop.
Cheers
Mike