There are many Sat Radio systems out there.. SOME are designed to plug into the back of the dash radio (I have that kind of dash radio) Some have AUX outputs (This is what I'd recommend in your case) that is basically either a headphone like jack or a pair of RCA jacks (WHite and red)
As for "A lot of battery".. Well that depends on how much you use it.
Motor homes, generally, have one of two house radio systems.. Some the dash radio has a switch (Main/Aux or some such) and can be switched between the AUX circuit on the chassis and the house battery for operation.. If you have this, then simply plugging in a back of the radio module and finding a spot for the antenna and flip the switch to use mains power.
Some (mine) have two seperate radios, one runs on 120 volt, the other is a common car dash type.. I'd need the "Line Out" type and the Aux In module for my radio (Which by the way I have, the aux in, not sat radio).
Some also have multiple modes.. They sell a "Boom box" Desk and Auto adapters.
The sat module snaps into/onto all 3 modules,, in "the desk mount it would feed your "House Radio" (120 volt device) in the Auto-Module your dash radio, and in the boom box.. Portable.
Check out the "Dock and Play" receivers on this page:
Crutchfield dot com