tweeters did xm in my last viper;  and they put it under the plastic in the
trunk;  over where the license plate is -  the very tail of the car.  it was
hidden by the carpet - you would never know it was there.  i never had any
problems with reception.    the product was the alpine xm/mp3/dvd head unit
for $399;  if thath helps.  don't remember the unit part number - sorry.

Someone stuck an antenna inside a rear fender a couple of years ago
don't remember the details.  The following scheme for XM results in
nothing showing except for the 'blister' antenna on the roof and a small
loop of co-ax right behind the driver's head.

Turns out that the hatchback hingeplate, aft of the hinge, forward of
the glass, had enough ferrous in it that the stock XM antenna sticks
fine.  Didn't budge on a desert run at 130 mph -- low overcast, no
planes in sight!  {{:-).

I placed the antenna about half way between the centerline and left edge
of the hinge plate (on the '89 the aux brake lite is mounted to that
hinge plate).  Coax lead-in rounds the leading edge of the hinge plate,
makes a very small slack loop (just big enough for the hatch to open all
the way) then ducks under the hatchback seal, is hidden by the seal
behind the driver, thence under the cargo deck carpet and into the
center console compartment through a hidden hole (only hole I had to
drill).  I ran a wire off the accessory circuit (passenger side fuse
panel) into the center console and rigged a small voltage regulator to
drop it down to 8vdc for the XM-Roady2.  The Roady2 fits into one of the
cassette slots in the console.  Everything can be pulled out without
leaving a mark. The FM re-conversion to an unused channel is good enough
for my ears so I've got no audio wiring. Having the outside antenna
closer to the rear fender radio antenna seems to help when Mexican
stations splatter onto the 'unused FM channel.'

An antenna is still inside the C5 and I'm using the accessory power
outlet in the center console -- doesn't look as bad as did the C4 before
I hid all the wires--so, "the power of laziness" rules and I've not
taken the time to put hard wiring and a regulator in that car.  C4
reception is slightly better with the roof mount and can make it through
some short tunnels on memory (no dropouts), while, through the same
tunnels, the C5 has a short gap in reception.

Also live in So.Cal where the satellite is strong.

HTH
--
PJ
'89 Hookercar '02 e-blu 6-spd coupe

I have an XM intenna mounted on the dash, over the crack on the right side
by the pillar.  Reception is pretty good, but cuts out in the mountains
(Central California).  I want to take it back and have it mounted in the
center of the dash up next to the windshield, but it looks like it might be
hard to get the wire over there under the dash.

Ed