I have 2 GTX (10.5' 2007 and 8.5' 2008) and i can say that both of them are great sails.
At first when i bought 10.5 i had porblems (cams were popping out of the mast while rigging, the broken the batten on the first derigging, on the second riggind the mast made a hole in the sail sleave, it went through about 20cm from the 3 cam), but after 2-3 rigging/derriging procedures i have found very simple and easy way.
I take the top peace of the mast and slide it through the cams all the way till the end, make sure that the top of the sail sits on the mast good. Don't be afraid of wrinkles, they won't do anything to your sail.
After that i put the bottom part of the mast and downhold the sail carefully.
Derigging is in the opposite way.
Take the boom out, release the sail, take the extension away, then take the mats (~the place where the boom was fixed) with your right hand, with you left one slide the sail towards you (the top of the mast). You will see that step by step the cam tension on the mast will become smaller and smaller. Ass soon as you'll see the mast connection by the downhold rollers take the bottom part of the mast and by holding the sail with the left hand pull the mast out of the sleave with your right one.
This works for me. Now i can rig and derig the sail only by my own. No other people needed to hold the top of the sail while pulling the mast out.
Sorry for my english.
P.S. 10.5 gtx is abit more complicated. After i push the top of the mast and put the bottom part I fix the boom (just putting it on so it could easy slide up and down) outhold the sail a bit and only after that starting to downhold the sail. This helps me to prevent the batten cracks. I wrote that the first time when i was derigging the sail i took off the boom first and when i realeased the sail and started to pull the mast out the 2 batten broke down.