After some more looking i have the SVN keyword substitution working. Quite simple in fact. On the working directory right click on the folder that contains all the DTSX files - mouse over Tortoise SVN - click properties. Click New then select svn:keywords from the dropdown and for the value entered "Rev" and mark the checkbox to apply recursive this then set the property for every file in the folder. At this point I did a commit since each file was modified.

I didn't worry about other files (non-dtsx) since the property will be there but it will not perform the substitution unless the specific string is found within the file contents.

Next opened the solution and set the value of the Version Comments property on each package to $Rev$

Saved all then committed. Checked the version comments and found the version number in the comments field. Very slick, now I can setup my logging to include the SVN version number.