FWIW, I too have used Brightside in SWFL, and the two-year life expectancy seems about right to keep its gloss. However, I extended mine for another year or so at a time by simply hitting it with some polish to get the top layer of chalked paint off. Probably would have lasted longer if I’d actually waxed it. And mine was a bright yellow (smokestack) where the chalking showed pretty badly; another color might fare better in that respect.
Also, reading the history of the famed Ticonderoga, when she was conscripted into the Navy for WWII, her captain slathered on several coats of varnish over everything before they painted the battleship grey, and was credited with ‘saving’ her. Apparently the paint came off fairly easily after the war and never got into the grain and ruined the woodwork.