I do the same thing as Lester on both a MTB frame and a CX frame. In both cases, the combo of rear fender and rack created a mess of metal at the back of the bike that rattled too much for my taste and looked awkward. In addition, the CX frame was missing the bridge between the chainstays, so I would have been a little short on places to mount a fender down there.
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--Ben
2006 Trek SU100, 2009 Motobecane Fantom CX, 2011 Motobecane Fantom Cross Uno, and a Bakfiets
Previously: 2000 Trek 4500 (2000-2003), 2003 Novara Randonee (2003-2006), 2003 Giant Rainier (2003-2008), 2005 Xootr Swift (2005-2007), 2007 Nashbar 1x9 (2007-2011), 2011 Windsor Shetland (2011-2014), 2008 Citizen Folder (2015)
Non-Bike hardware: MX Linux / BunsenLabs Linux / Raspbian / Mac OS 10.6 / Android 7