I have my Sirius (magnet mount) antenna up under the luggage carrier.
Perhaps differently than others, I put it at the extreme leading edge
of the carrier. Even with luggage in the carrier the signal isn't
blocked (only bridges and very tall trees manage to block the
signal). The cable is plenty long enough.

> I bought a cheap XM radio kit that -not mentioned in
> the specs - comes with a portable magnetic mount
> ground plane type antenna. Not exactly a perfect match
> for a Westy.
>
> Just sitting up there, stuck onto one of the luggage
> rack tiedowns, it does seem to work in my driveway,
> but I am sure its not optimal. Would reception be
> better if it was mounted on the steel roof, but inside
> the fiberglass?
>
> We are leaving on a road trip Friday, and I consider
> the installation experimental, so I don't want to
> spring from a $100 marine antenna, at least not yet.