Humidty

I'm in the process of purchasing a Mainland mahogany tenor and have a few questions regarding humidity.
Next year we're planning on moving up north to the Kimberly in Western Australia (here) not sure where we exactly it all depends on where the education department places us. I'm a bit concerned about the ranges of humidity, depending on the location the relative humidity throughout the year can be between 74% - 45% or 71% - 28%.

I'm worried will such large fluctuation through out the year cause much problems and what would be the best ways to help?

Generally, you should try to keep the RH at around 50%. Get a good case if you don't already have one. Use an in case humidifier in low RH conditions. I like the Oasis humidifiers that are suspended into the sound hole. You should also consider a hygrometer (I use an Oasis, in-case hygrometer) to monitor the levels. Low RH is potentially more dangerous than high levels, but when it is very humid, you can use silica gel packs to soak up some of the moisture.

The large fluctuation is not, in and of itself, a problem since it is happening over a long period of time.