All attempts to customize Apache log fails

This should be very simple, but every attempt I make to modify the log string is causing either apache to not start up or logging to stop altogether.

I've tried the following combinations:

# I have a few of these, but testing is being done with just this one for now
SetEnvIf Request_URI "^/robots\.txt$" dontlog

CustomLog '|/usr/sbin/rotatelogs "/var/log/apache2/www accesslog" 2592000 -420' "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\"" combined env=dontlog

CustomLog '|/usr/sbin/rotatelogs "/var/log/apache2/www accesslog" 2592000 -420' "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\"" env=dontlog

CustomLog '|/usr/sbin/rotatelogs "/var/log/apache2/www accesslog" 2592000 -420' combined env=dontlog

These and others I've tried all fail. I have even tried using LogFormat in conjunction with CustomLog.

Has anyone successfully used the combined format with some conditional env vars?