MidMac is for sure a good organization, but before you sign a contract you should have checked each and everything... u must be an experienced doctor why dont you try to negotiate the accomodation status, as I have heard from many that Portacabin life is not so good...

or else.... give it a try for few months and then after a while speak to MidMac management again....to increase your salary & accomodation status
best of luck!!