That's not normal. We live in our rig for 4 months/year next to the Gulf. When I turn on our dehumidifier at night it will start off reading 80-90%, by morning it's at 50% with a full tank of water.
You'll have mold in the window tracks because of their poor construction and the condensation that is created. You need to be vigilant on keeping those clean.
Do you have any delamination on the outside? If not then you need to be vigilant about keeping humidity out of the rig. Showers and cooking need to be vented out when they occur. Just leaving a roof vent cracked open an inch will help a lot.
Keep us posted, I would love to know what the real cause of the problem is.