I can only give you my opinion based on using both 303 and wax over the last 30 years, not scientific data.
303 is a great protector against UV damage. It works really well on inflatable boats, maintaining plasticity. Make sure that the inflatable is clean when you apply. Ideally keep the inflatable covered from sunlight even when using 303. An old cotton sheet is all that's needed. The inflatable won't mind getting wet if it rains but it will love to breathe. Use the 303 whenever the inflatable looks dry. Apply and then make sure you use a cloth to remove any excess.
On fibreglass you get a nice shiny finish that does give UV protection, albeit very short term. The effect lasts only a week or so, especially if your boat is kept in the water. The temptation is to apply excess in the hope it will last longer. The 303 becomes sticky and attracts salt, dust, sand etc. that effectively becomes a micro grinding paste, especially behind fenders.
Thinking of fenders, 303 is great to apply to clean fenders. Used correctly, no excess, it keeps them plastic and slippery.
To protect your hull use a good quality wax directly on the hull after polishing. I'm not sure how adding wax over 303 will work. Most likely the waxing will remove the 303.
Hope this helps
