This is what I have in my USRENV.dcls:
catia.MODEL    = '$HOME/db';
catia.MODEL    = '$HOME/db2';
catia.MODEL    = '$HOME/db3';

These three lines let me use /home/catadm/db, /home/catadm/db2, or
/home/catadm/db3 in pcdmis

In my catia.dcls, I have the following:
catia.model = '"$HOME/db", "db"';
catia.model = '"$HOME/db2", "db2"';
catia.model = '"$HOME/db3", "db3"';

These let me use db, db2, and db3 from pcdmis.