Oh you been to Halong Bay before liao, then no need to go again lah I think. Not much difference from winter and summer.
Enjoy your December Sapa trip!
Did you visit perfume pagoda during your last visit? There are mixed reviews about that place. I have visited tam coc and i am wondering whether the two places have similar scenery.
Did you stay in sapa for 3d2n or 2d1n? I have chosen the 2d1n bus tour to sapa cause i am lazy to walk for so many days , the scenery gets boring after 2 days and the train journey is too taxing.

What is the point of paying money for holiday when you spend so much time on the bus, plane or sleeping inside hotel room?