If under your hood means your convertable top then yes you will get a useable signal. Metal roofs and engine hoods will block GPS completely.

My GPS unit's antenna is actually inside my dashboard, underneath the plastic covering, just above the heater vents, as shown by the red circle here:



It works perfectly, the plastic doesn't block the signal much, and neither does the windshield. If I'm not inside a garage, I can get at least 5 satellites locked almost all of the time.