It rains a lot in N. Vietnam, in fact from December to April the clouds almost never lift. Also it gets cold, much colder than you'd expect. We all think that Vietnam is tropical, but in the north it is more subtropical. The best weather is in late October to mid December - so take some rides in the autumn while you can. You could take a trip north to the border perhaps.
As far as bag checking, isn't it ironic that you have uniformed men pawing through your bags as you leave "the free world" but when you come to a one-party state, no body even takes a peek as you walk in? I wish you luck in getting the kind of bike you want, it can be hit and miss sometimes.