I'm James, a real estate broker from Charleston, SC. You can rent out a house for as long as you like in Seabrook, Island. There really is no limit as long as all parties involve agree on the specifics. Peak season is during the summer months when everybody just wants to get out there and enjoy the surf and the sun.
I have properties in Seabrook if you are interested, you can just check them out in my website: http://searchrealestate.co/. Contact me anytime if you have any questions.