Where best to put local modules?

[Zentrader]

Wherever it is physically located, I would suggest linking the dir to /
usr/lib/python/site-python (on a Linux system).  AFAIK the sole
purpose of this dir is for the type of thing you are describing.  On
my system it also gets copied when Python is updated.  What
permissions you give the dir is up to you.  Also, you probably want it
somewhere that gets backed up routinely or you may loose your latest
and greatest version if there is a crash, etc..