Can you let us know which seats on the Marlin side are in the shade?

No shade on the Marlins side that I could find as of last season. Maybe they undated in the off season

The party deck is covered and with fans on all game. But as for shade there isn't much to speak of, best bet is get tickets in the infield and the concourses are covered and shaded, you can duck into those intermittently to cool off. Midday sun is directly over top just bring plenty of SPF and run down to the concessions in the concourse under the stands once in a while, you'll be fine.