That corrosion almost looks like chemical attack rather than plain weathering. Either way, if you want them to not rust, which doesnt hurt them as far as strength goes as it would take many years to rust away the bolt heads.
To really preserve them, remove them one at a time,clean all the rust off, coat threads lightly (a little bit will do) with heavy grease and reinstall. Tighten as specified for max torque per bolt size. After they are all removed and reinstalled, then solvent clean the exposed surface and paint to match the equipment. It should be good for several lifetimes then. The grease will protect the internal threads and paint will seal and protect outside surfaces.
If bolts are susceptible to loosening off, finally after the paint is dry, take a good paint marker (Nissan makes good ones in all colors) Mark a straight line across the nut and bolt with a contrasting color. Then note on weekly inspections that the line is still straight, if not then nut has loosened off.