Hi Farflung
There are many providers who do offer Annual Multi Trip travel that covers up to 60 days, off the top of my head I know that Club Direct do. As far as deciding if you really need business cover only you can decide that but to gain peace of mind just check through the policy wording or give the provider a call, from what you are saying though the duration of stay is the issue, if this is the case then regular insurance should be fine.
good luck
Maxine