Hello Dahillbilly,
I just installed two Maxxair Fanmate covers on our 2019 Big Horn this week. Our trailer is about on year old, but when I accidentally leaned on the bathroom fan (not a Maxxair or Fantastic Fan), the lid was so brittle it broke in many places. We're in Washington State, not known for high UV issues, but the lid was very brittle after a year. I've ordered a new replacement Camco hood for that, but my point is that adding the extra hoods would decrease UV decay of your existing covers. We've installed hoods on our last three trailers and consider them a necessity for all of the reasons others have given you on previous replies. I chose the Fanmate hoods this time because I imagined that they would give the fan hoods more room to rise when I opened them. It doesn't seem to be much different than other hoods I've installed. The fans still hit the Fanmate covers when I attempt to open them fully.