If you paint it, you will always be painting it. When you sell it the owner will wonder what your hiding under the paint. On mine I only spray gray primer on some of the small rust spots so it blends in and looks better. It protects it too from corroding quicker. If your in salt water Galvanize will last lots longer then steel trailers. Even in fresh water steel trailers rust big time. The pretty looking trailers look great...till they rust. You have a good trailer don't cover it up by painting it. It's a trailer...not a show piece. Save your efforts for waxing you seadoo instead.
You should add your seadoo model and year in your avatar for future questions.
Karl