The most important consideration is cleanliness and lubrication. You should rinse your tackle completely after each trip to the coast, even if you've been fishing in brackish water that is more fresh than salt. Rinse the reel thoroughly under a soft stream of fresh water rather than the hard spray from a hose nozzle that may actually push saltwater into the reel. Some reels, like the new Penn International baitcasting series, actually have drain holes at the bottom of the side plates. Baitcasting reels require oil more often than spinning reels if they are to perform at their best.
Heavy oil is a no-no for baitcasters.
It reduces spool rpm and can eventually gum up the works as it collects dirt and dust. Oil should be applied to the bearings and cups at the ends of the spool shaft, the levelwind mechanism, and any other moving parts inside the reels. Oil the handles if not turning freely. It's a good idea to always keep a small container of lube on hand. During a long day of hard casting, you might want to add a drop to the bearings and the levelwind before the day is done.