G'Day Mark,
There's obviously a lot you can do with active cooling and SCT coolers etc. I can't answer your direct question there, but if you will have the C11 installed in an observatory, a humble small electric fan blowing ambient air over the OTA will help
heaps without the expense of an SCT cooler or active cooling fans.
I was very disappointed when I first got my C11 to find that an hour or two of cooling still resulted in strong thermal currents in the OTA, when they would've been long gone in the C8. I tried the electric fan blowing across the OTA, and ever since I haven't seen evidence of a tube thermal. There obviously must be early on, but its a low tech solution that is worth exploring.
Al.