[glend (Glen)]

The steel tube RC 12 is known to be susceptible to temperature changes (thermal equilibrium) which will affect focus. I had a RC 8" and it would exhibit focus shift due to temperature changes.

TS still sell carbon tube upgrades, if you really have to have a tube 12" RC. It might be cost effective to just buy an empty carbon tube ( bored for GSO 12" components), and then buy the 12" RC from Andrews here in Oz. Shipping cost for TS, for a complete RC12 would be significant ( add GST), but a bare tube should be cheaper all around. If they still sell them.
My overall experience with GSO RC is that they are a budget scope, Don't expect Planewave quality, they are a project.

On checking, I see Andrews in Sydney are selling the 12" steel tube RC for $1699, which is very cost effective compared to price history on this model ($2500), and may show it is not a popular buy. If you had it in an observatory, and we're content to allow significant temperature equalization time, and used a focus motor system to refocus for temperature variations, then it seems like a good buy, to me.
I assume you know this is an imaging scope primarily, there are better choices if your visual. Finally, it is heavy, being steel, so you will need a significant mount, one capable of imaging with a minimum of 25kg load.

Update: just checked with TS, they still offer the 12" GSO bare carbon tube upgrade for 748 Euro, but shipping cost would add 190 Euro to that, if you choose that path.

If your just starting out with imaging there are better choices, like fast Newts.