Maybe it has to do with location, but I always left my "boat tools" on board and mostly in the ER. Never had any rust to worry about. However, despite living in a "rain forest", I always kept the boat warm and dry. I always used an oil pan heater, which besides keeping the engine warm, also kept the ER warm and dry. In the winter, I used a dehumidifier and several fans to move air around. My engine showed no rust, and nothing else in the ER showed rust either. One exception. Previous owners allowed the raw water pump on the generator to leak onto the sound shield floor, causing that to rust. I removed what rust I could and coated all of that floor with Rustoleum paint followed by an application of Boeshield. I also repaired the leak.