In-dash Navigation / Radio Options in a Class C

Here's the complete wiring book for your unit. Look thorough it and you may find some channels that already exist but not being used where you can fish a wire through it.

WF331C - 2007 -

There appears to be a some sort of satellite radio antenna hookup. Often the wires are installed from the roof to the radio (especially of OnStar equip), just the antenna and connectors are missing,