Hello,
we will be cruising Thailand, Vietnam, Cambodia and will be taking independent trips and tours staying overnight in some cities. This question is about visas required for US citizens, please provide your feedback.

The first port in Thailand is Koh Samui followed by Bangkok(LAEM CHABANG) the next day. Being US citizens we don't need visa for Thailand. Is that correct?

The next for us is to fly independently from Bangkok to Siam Reap, Cambodia. We will stay in SR for two days. We do need Cambodia's visa and can obtain it online as evisa, right? we understand we can get it at the airport upon entry but want to save time.

From Cambodia we will fly to Saigon, Vietnam, stay there in the hotel for 1 night and then will re-join the ship. We will be cruising more ports in Vietnam, and possibly will go overland/overnight in Hanoi.

Can we get a single entry evisa for Vietnam? Will it be ok for every port and overnight in the hotel in Saigon and Hanoi? From what I read it seemed to be fine but I want to make sure.
Appreciate any comments/feedback on visas.

You might want to also post your questions on the Asia forum since there are many regulars there who know everything about travel all over Asia and seldom if ever visit the Cruise forum.

HappyTrvlr,
do you think we need multiple entry visa or single entry? Single entry can be done via evisa, multiple entry is a different story.
I thought since we enter Vietnam in Saigon and then stay in Vietnam (though travelling on the ship) we can obtain a single entry and therefore evisa will suff

Forget asking here. Check with the State Department, the consulates of each country involved, and with the cruise line. If any document is missed or is the wrong type, you will surely miss any land excursion that includes that country and the cruise line may even deny you boarding for the entire cruise. And don't forget any country where your plane may stop while you are in transit but not leaving the airport. You may still need a document for that country.