With proper preparation sailing in sea water should be not be a significant issue.
Some simple precautions would include:
Putting your receiver inside a balloon sealed by a wire tie - same thing to your battery pack.
You can water proof your servos with some silicone sealant, or the liquid electrical tape products.
Make sure your hatch is properly sealed and there are no places for water to get inside the hull.
Put some pieces of sponge inside the hull to absorb any water the may find it's way inside.
Put some flotation foam in the hull. Must be enough to keep it afloat if the boat were to fill with water.
Fasteners that are not stainless should be painted or sprayed with a silicone spray or light oil to prevent corrosion.
After use wash the boat to remove salt residue. Remove the sponges, check for any water intrusion, clean parts that may have
gotten wet. Pretty much the same prep you'd do in a full sized boat.
Windchaser