We have come back from Vietnam where we finished a wonderful kayaking trip in the bay named Ha Long (Dragon):)
The travel agent was great when they arrange smoothly services with the guide (Coung) who was very professional, hummor and friendly. We were conducted to visit many amazing caves and lagoons. Some of them are named in Vietnamese, very difficult to pronounce (Haeng Doi, Da Be...).
I recommend your trip's lenght should be at least 04 days in Ha Long if you have a chance to go there. Because you can go to very beautiful places where few tourist stay.
In this trip, we were very lucky when saw a group of wild monkey and some special mokeys (the guide called them as Aisa monkey)
If you want to do a kayaking trip in Vietnam, I recommend you contact with Seacanoe Vietnam (Inserimex Travel).