Personally I found that this script works better than the Root External 2 Internal SD because the remount happens while the phone is booting. Not after the phone has booted.
Your storage will be reset if you mounted your phone as "Mass Storage"!
Do NOT mount your phone as Mass Storage if you use this script.
MTP and PTP mode works fine.
1. Partition your internal storage. I use 11Gb~12Gb Pit file.
2. Flash your custom ROM
3. Flash Attachment 2545298
If you need to trouble the script
1. install Root External 2 Internal SD
2. Find out the mounting point of your internal storage and SD card. They should look like