MBColo303

Can anyone tell me where the Sirius SDAR control unit is located in my 2009 C300 Sport 4matic. The message on my screen says "No Service". I can't even get channel 184. The dealer tells me that there is a short in the unit and it needs replacing. Only problem is they want $1300 to do it. I know I can buy them online for $500 to $700. I'm pretty handy so I thought I'd try and replace it myself. I'm pretty sure the unit is in the trunk area, but any help on locating it and then replacing it would be appreciated. Thank you.

Gcarpenter

See attached.