Many of the high end boat trailers use a cover plate over the wheel hubs to improve looks and protecion. The problem that arises is the bolt is made of stainless steel and they screw into the aluminum wheels. With two disimilar metals, it isn't long before corrosion sets in. Take the time to unscrew the bolt and use some anti-sieze compound on the threads once a year, thus eliminationg the corrosion.
It will save you a major headache on the road should you have a flat.
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