'71 Blazer floor pan ???

I'm about to cut out the rockers and floor pans to fix the common rust problems. I need to know where all I should brace it before I start cutting so it doesn't flex. The top and doors will be off it. Please help, thanks in advance.

between the door jams and fire wall and back wall. make kinda a tic tac toe board in there lol.

May want to check out the rocker box also, for rust.....