So I asked my cat and he pointed to this web page:
http://timgeerts.blogspot.com.au/2009/10/msiexec-installutil.html So you have to put /logfile="C:\temp\mylog.txt" in the CustomActionData property in the project. This is ugly and can probably be made more formal and neat later, but at least I can see my tracing now. The installer is surrounded by confusion -- Greg
