GPS inside or outside of the body?

I’m wondering how much signal loss I get, if I mount my external (HEREE+) gps inside my aircraft body? Or it wont affect much?
Body is laminated from fiberglass. I could use carbonfibre on top of gps if that would imrove the work.

Carbonfiber blocks GPS signals AFAIK.
Fiberglass does not block GPS signals AFAIK.