Mice, my previous Forrest River Solera had a super highway open underneath that allowed them to get inside our cabinets. Poop and pee all over out pots and pans. I crawled all under the rig and finally spotted where they failed to foam fill one 2x2 area. I stuffed it with copper mesh and sprayed a liberal amount of black foam in there. No more mice in the passenger area. But the MB Sprinter chassis diesel left a nice path for them to build a huge nest in the engine air inlet. They also chewed a few wires under the hood.
So we built a building and parked it inside. No more mice issues.
Other than that, things have been pretty good over our 9 years of camper ownership.