Simple / Stupid File Permissions Question

[Paul Lathrop]

I have a simple/stupid question regarding permissions.

What I would like is the following: I have a directory called group_dir 
that I would like all members of a group to be able to work in. 
However, I find that whenever someone creates a file in that directory, 
it is not set group writable. I know the user's umask setting affects 
this, but I don't want to change that - then ALL their files would come 
out group writable. Basically, I want all files in group_dir to be 
readable and writable by group members by default, including newly 
created files. Is there a way to do this? I thought up a kludge to use 
cron to periodically run chmod -R... but that is so ugly I don't really 
want to do it that way.

Thanks for your assistance,

Paul D. Lathrop