Below is a link to a site in Perth - actually Fremantle - I have met the bloke Tom and had a look at his ovens, I have also cooked in one and it was terrific. I am seriously thinking about getting one as I am moving to a new house in a couple of months and a wood fired oven out the back would be brilliant - got to do paving and pergola first - actually got to get a job first....
Anyway check this site out and also have a look at the guides to building the DIY oven including the base which sounds and looks pretty good. It seems he has outlets in other parts of the country. If youre ever in Freo go and say gidday to him he is a bit of a character.
http://www.woodywoodfiredovens.com.au/
I am thinking the way they do their base using patio tubing is alot more straight forward than the way you are doing it Gregs??? But would you still need to pour a slab for the base to sit on??