I currently have a single entry 1 month visa for Vietnam. I plan on going to Cambodia by bus, and then flying back into HCMC Airport from Cambodia and then continuing on to my flight back to the US. Do I need to get a multiple entry visa if I don't plan on exiting the airport on my way back from Cambodia? I will have checked luggage, so would it be allowed to pick those up and then go back and check in for my flight back to the US? Thank you!