Caution: I have rooted my device for the first time, I have no prior experience in rooting. Continue at your own risk.
I am not sure about the RAM part, but we can flash the custom ROM from the internal SD card too. The following link is for explains the installation process for Installing CM 10.1 on Galaxy Tab2, however, we can follow the same steps for GT-...
Here the simpeline
mount -t ext4 -o rw,noatime /dev/block/mmcblk1p1 "$REALMNT"
sdcard "$REALMNT" /storage/extSdCard 1023 1023 &
And here writable ext4 on external sd
chown media_rw:media_rw /mnt/media_rw/extSdCard
chmod g+w /mnt/media_rw/extSdCard
You can change "extSdCard" like "...