I talked to several local Fla. LEO's (police and sheriff) and they all said that as long as the weapon cannot be readily accessed (even an unlocked glovebox is okay), it is permissable. Even a zipped closed gun rug or an unlocked (but latched) gun box is okay. I have driven home from the range more than once with my XD-40 in its case, unloaded with 2 full mags, sitting on the seat beside me. And I wasn't worried.
Now, if you have a carry permit, you can have that sucker hidden under your dash, tucked between the seats, or in a door tray, fully loaded and ready to fire. Just make sure you're carrying your permit, or it won't be pretty.