i went to the DR in July this year and i took my GHD straightners with the correct adaptor, but because the GHD's dont have a voltage switch, they didnt get anywhere near hot enough to straighten my hair. i'm not even sure if straightners even have a voltage switch, as they need to get very hot to do their job!
So ultimately i had to either tie my hair up every night (its shoulder length), or i too put up with a mass of curls, which on some nights when it wasnt too humid, didnt look too bad!

So best bet is to leave the straightners at home and think of ways to jazz up your hair with bobbles, clips and hairspray!!
good luck and have fun X
TallulahJ