I installed my Sirius radio in my truck using the FM modulator method. Like YWORRYDOG, we also listen to that Sirius radio on the CD/radio inside the TM. The only problem I found is that the remote control to change stations on my Sirius is not powerful enough to reach through the TM and intom the closed truck. I have opened the slider window on back of truck and got it to work, but it's not convienient.
This is not a problem if you listen to just one Sirius station. Of course you can still tune into as many regular "over the air" radio stations as you want from inside the TM and flip back to that one Sirius station anytime you want inside the TM.
I don't recall what model my radio is, but it came with a tiny remote that uses a small coin size battery. A radio with a larger remote with AAA or AA batteries might give you enough power to flip the Sirius station from inside the TM.
Or perhaps a programable replacment remote? I will need to look into that for myself.
Jim