I was able to get write access working by either mounting manually MyDocs using dmask=000 and fmask=000 options.
I also tried using only option uid=29999 that seems to work as well.
It does look like the mmc-mount script is not able to utilize any of the vfat-opts from mount-opts?
vfat_opts="$fat_opts"
(If you try "mount | grep MyDocs" this should show all options that were used when MyDocs was mounted?)
grep MyDocs /proc/mounts