Problem starting VNCServer at boot

[Tom Smith]

ENVIRONMENT
FreeBSD 4.8-STABLE
TightVNC 1.2.8

PROBLEM
Getting error: "Starting local daemons:vncserver: couldn't find "xauth" 
on your PATH."

SITUATION
I installed tightvnc-1.2.8 from the port collection and configure 
/etc/rc.local to start a vncserver for a specific user at startup using 
the following command:

su <username> -c "/usr/X11R6/bin/vncserver :1 -depth 8 -geometry 800x600"

When this tries to start at boot up I get the above error. If I start it 
from the command line it works fine.

This sounds like an issue with the defined PATH at bootup but I've not 
been able to find anything explaining how to define this PATH in the 
FreeBSD handbook or otherwise.