I also purchased the SVX300 and initially placed the antenna on the dash. Travelling north, no signal at all.
I then routed the cable up the driver side door molding, and up the inside wall, placing the antenna on a magnetic plate stuck to the interior ceiling. No drilling to the exterior, and it works perefectly.
2016 Greyhawk 29 MV
West Branch, MI
Wife & Co-Pilot: Famous Amos
1 Shizu, 1 Havanese