I guess it's time for a new bio since I've had the other one for eons. Head dev of Insolence, I have some very limited experience with coding, yadda yadda yadda.
It's not even close to seamless, and I didn't get all of the pink out. I'm gonna have to redo this sometime.
I would suggest checking with materials\Environment maps\citadel001 for references on how exact skybox sides looked like (you'll have to use VTFedit to switch between the cubemap's slides). I mean the cubemap is hilariously small, being 64x64, but you could make it out what clouds looked like. Sorta. You'll still have to fill them on the texture manually but you'll now that here's say a dark gap and there are two bright stripes and such, and what the X'ed parts were like. And if you look at the Citadel concept you can see what _ft, _rt and partly _bk parts should look like.
Yeah.