I'd appreciate if anyone who has a Core XY based printer would chip in with some insights.

I'm thinking of building one or two new printers (one for me, one for a friend) and the Core XY concept seems pretty good, it would allow me to install all the motors on a fixed place simplifying wiring, reducing inertia, wear etc, etc...
It all seems very good, but I wonder if there are some problems with that configuration, for example if the long G2 belts would stretch, or cause rippling due to resonance. Also I'd like to make an enclosed printing volume, so that the temperature can be controlled, I don't know how the belts would fare at 60 or 70 degrees C.