We intend to spend about 3 weeks in Viet Nam and Cambodia in February(2012). We will initially enter and spend a few days in Saigon. If we then take a boat trip from Saigon up the Mekong River to see the ruins at Ankorwaht(sp?) for a few days will we need additional visas or other travel documents to enter Cambodia and return to Viet Nam? We also want to travel to Phu Quoc island for a few days...will this require additional travel documents?