hay buddy try this,
I use fire brick, on the bottem and standing up on the side now you can get F B at a builder supply or tractor supply, standard 31/2 x 6 x 1 thick and cut them down to fit or call a refactor supply (thay rebuild furances in factorys n schools) you can get bigger sizes or thay can cast the size you need,($$$ i'll cut them to size!!) than use wood, now remeber if your cooker sits in the sun n out of the wind and gets up to 120 deg.with out any fire you only have to bump it up to your desired temp. two ways i do use the wood (1) if it's good,dry n seasoned i'll burn it in the fire box,, but i use an offset fire box. (2) but if it is not seasoned or damp i'll burn it down then shovle it in the fire box and if you use fire brickyou won't burn out the bottem and the brick holds the heat for hrs let us know how it works