do fluids do any harm when left in too long?

When I said it ilkely is fine, I was serious. I have vehciles that don’t get driven much that haven’t had an oil change in years or a decade. They’re fine. Also have engines that get low hours per year and I wouldnt think of not changing the oil before layup. And others that I change after every or every other use.
But if you care about the RV and plan on keeping it no sense in procrastinating.