Mounting GPS/antenna on Carbon panels

The Volkslogger manual states that 'During installation,
assure that the integral antenna has a clear view of
the sky and is not shielded by metal or carbon fiber
parts.' (there is no similar comment in the Colibri
version 3.0 manual.)

Has anyone with GPS units mounted on carbon panels
encountered reception problems? Would a carbon pannel
interfere with reception if the back of the GPS antenna
is flush against a carbon pannel even if the top of
the antenna still had a 'clear view of the sky' vertically
upwards?

Does anyone know if there is an external antenna option
for Volksloggers? Also, now that the Colibri seems
to have a built-in antenna as standard is there an
external antenna option for it also?