The sun would be affecting the interior
fiberglass if the interior fiberglass were exposed to the sun. I don't think the sun shines out of your 'glass.
The cabinets and such might get a bit more sun there than back up here in MA, but the higher summer sun angle nearer to the tropic of cancer would mean more on the roof, less in through the sides partly negating any increase in intensity. More hours of daily sunlight as one moves further north also offer some compensation for a lower sun angle.
So FL sun vs. MA sun would be less of a factor than any of a number of other possible odor sources.
Freon is relatively odorless, and as it's pressurized it'd leak regardless of the hour of day or
solar gain. Your AC would soon cease to operate when the pressure switch tripped open. You didn't mention those issues so I'm claiming freon isn't a source.
On a day off from your work, stop by a boat repair shop and ask to get a sniff of fresh fiberglass resin. See if that matches your 'chemical/plastic' smell.