[Antennas] Throug Glass Antenna information?

[Mike]

I have two Larsen through glass mount antennas
(one 2 meter and one dual ban) on my SUV and
I am having trouble with RF getting into my GPS
receiver.

The question is, I know the loss on this type of
antenna is high (not sure what) but does it also
allow more RF inside the vehicle than a outside
antenna would?

Anyone have any experience with these or any
information (or links they can point me to)?

Thanks

Mike KU4ZD