The biggest thing you can do to protect the interior is cover the camper. While in storage the most damaging thing will be sunlight shining through the windows and roof vents.
You may think that not much gets in but it adds up over time.
In the 10 years we had the 5th wheel I had to replace all of the roof vents, the bathroom skylight turned yellow, and all the interior fabrics (curtains, upholstery, wallpaper, etc.) faded or changed colors all due to sunlight.
For our Axis we're covering everything we can during the summer (keeping roof vents plugged, covering front windows, etc.) and during the winter the whole camper gets covered.
You may think that not much gets in but it adds up over time.
In the 10 years we had the 5th wheel I had to replace all of the roof vents, the bathroom skylight turned yellow, and all the interior fabrics (curtains, upholstery, wallpaper, etc.) faded or changed colors all due to sunlight.
For our Axis we're covering everything we can during the summer (keeping roof vents plugged, covering front windows, etc.) and during the winter the whole camper gets covered.