We never covered our 5th wheel. Over the 10+ years we had it: All the wallpaper inside that was exposed to sunlight faded, the vents on the top became brittle and cracked (requiring replacement), the outside decals all faded and peeled off (I know you don't have decals with the HD-Max).
Our Axis I've been covering it over winter, and during the summer months all the windows are covered with foil, and the inside of the vents are covered to keep the sunlight out. So far, after 3 seasons, our Axis looks brand new (there is another one in our storage lot that doesn't get covered so I'll have a reference over time which one looks better...so far you can see that ours looks a little better..but then I'm biased aren't I
).
In the long term UV is the camper's worst enemy; do whatever you can to protect against it.
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