Oil painting in coastal environment
Oil paintings can be damaged by salt air and humidity. Other concerns are exposure to natural light, and sharp changes in temperature that can cause the paint to expand and contract and potentially crack or chip.

Rare and valuable paintings are kept under controlled temperature and humidity conditions and protected from natural UV light. 

Two things that you can do to protect your painting are to keep it out of direct sunlight, and frame it with glass.  There are two things to take into account if you protect your painting with glass, (1) the paint must be completely dry, and (2) the pane of glass should not touch the painting.

Please see a similar Stack question with mention of glass placement over an oil painting: Will putting an oil painting under glass cause damage?