Insulation is a must in my book, especially in QLD.
Check this thread.
Fire wall lining
Also think about ducting some fresh air into the footwells from brake duct vents etc. This is probably the best thing you can do with a Cobra when driving in the QLD summer. Heat eventually soaks through, no matter how much insulation you use. Well actually it's the 2nd best thing, air con is the best thing.