The Digital Dakota's seem to be a problem for most everyone. From what I've gathered it is partially because they are powered. They end up over-driving the amp to the point nothing comes in. The amp already has an fm preamp. Secondly it is because the signal is blocked due to metal interference. The best place to mount them is as high as possible above all metal. Basically on the faring.
That said, however, the best hidden antenna to use is the Tune Trapper (
http://www.ecshylites.com/page/page/603561.htm). I installed one on my bike and haven't had any issues whatsoever. I was skeptical at first, so I did a somewhat scientific test before I committed to the install. I put the bike inside a closed garage that is under my 3-story brick & steel house and closed door. With the factory antenna I counted every station I could receive (25). I then installed the TT antenna. I can pull in 27 stations with it in the exact same location. In my particular circumstances the TT is better than the OEM external antenna. The stations also come in clearer and stronger. The radio is much better now.
Here's a pic of where I mounted it on my 09 SERG. Notice how it follows the curve of the faring. It can be bent up to 30 degrees on each end no problem. It can easily be mounted above everything else. It's also completely waterproof.