Kosher salt ,morton and marine salt for cured meat?

HI im leavin in japan,and im curin meat....i heard i should use only kosher salt or morton....where is the problem with sea salt? is the iodine? i cured with sea salt ,and i got nice stuff maybe a little salty....can i use rock salt ?because here i could not find these kind of american salt,on the internet all the recipe for cured meat call for kosher......help please