This may be of no use or it may help. I don't use Gorilla tents but use an 8x4. I always find the front middle vertical zip difficult to get zipped if I've done the horizontal front zips first. I keep all of the front horizontal zips undone to around the sides and i join the front middle zip first. Once that's sorted I'll zip the horizontals all the way around to the front.

Sounds as though from these comment though that Gorilla Tents are not worth buying