are the serial numbers important? If they are, there is no getting around the amount of room that the report is using. If they are not important, you can suppress the details, and only display the information that doesn't change.
On second thought, if you want the serial numbers, but they don't need their own line (for each serial) you could 1) create a variable that appends the serial numbers together and only display it in the group footer or 2) make the detail section multi column and only display the serials in the details.
Hopefully one of these ideas will work for you.