I just got the glasspack for my beast, and when you look into it it has a bunch of raised areas inside. When you look at it from one end it would look like the exhaust would just go over the raised areas, and from the other side if looks like the exhaust would would be directed into the fiberglass. Does it make a difference which way it goes on? 
No directional arrow on it that I can see. I would think that the exhaust should be directed towards the fiberglass to help muffle the exhaust noise, but it wouldn't be the 1st time I was wrong. 
Figured I'd better ask before I clamp it on.Thanks
Mark
Next I called a little Mom & Pop Shop in town and was told it could go either way BUT if I put it in where the exhaust went over the the raised areas, it wouldn't be as quiet, less back pressure, and would last longer. This sounds like more of what I'm after. Putting it on so that the exhaust goes into the the raised area and right into the fiberglass will quiet it more, create some back pressure (though probably not noticable) and would definately burn out quicker. He recommended the way Will said, going over the raised areas. So I'll follow Sid's advice and try it that way, if I don't like it I can always unbolt it and turn it around. I also have an e-mail into the manufacturer, but I doubt I'll get anything back until next week. If anyone is interested it is a 12" glasspack with 3" inlet/outlet tips. I got it from JC Whitney, the part # is WF222826P.