I can't speak for your boat specifically, but typically GPS antennas aren't super-sensitive to location. You can even mount it under the helm as the signals will penetrate fiberglass.
The manufacturers will tell you to mount them as high as you can with a clear view of the sky, but having installed maybe 100 GPS's over the years I've found you can get away with quite a bit with them. Generally speaking, so long as it's not blocked by something metal or near anything that might give off RFI you'll do fine.
If you want to test it, just temporarily tape or zip-tie it in place and go out for a day to see if it works.
Don
'01 22 Classic, 502/B1
And a bunch of other stuff
"If everything seems under control, you're just not going fast enough" - Mario Andretti