its a big project.. not for the faint of heart.. i used to do rust resto's for a living...
it wont just be a matter of "replacing it with stainless"... unless you want to do a full custom fab like JJLaughner did when he went with diamond plate. thats alot of custom fabbing and much more inclined to be on a non street driven vehicle... not even sure how you would weld stainless patchs.. believe me, you'll have enough difficulty just getting stock replacements in and they'll last plenty long if done properly....
generally the easiest way to go is replacement floor pans.. i have a full set down in the garage.. they're available from lots of places.. its the import stuff, factory GM would be preferable, but good luck finding those.. the bed section of aftermarket stuff is decent, but the front sections are not direct replacements..
the best way to do it is cut out all the sections you want to replace fully, then sandblast the surrounding areas that you'll be welding to.. zinc all the bare stuff and use weldthru primer on the weld areas. a large portion of the rear bed is bolted in, usually to the wheelwells, the front, and along the qrters.. you will also need to transfer the under supports over to the new sheetmetal, so its best to check those out underneath.. the rear support (tailpan) will need to be replaced 95% of the time.. the other forward supports are not available afaik and will need to be swapped over... its also the time to do bodymounts, which will more than likely be hammered if the floor is that bad..
if you have a ton of rot behind the the front seats where the floor steps up 6"s or so and bolts to the rear floor section, that may be an issue.. i have not seen front panels that go back that far.. the front replacements go up under the pedals and most of the way back the door, but don't have that section behind the seat..
a search for "blazer sheetmetal" should turn up a bunch of stuff on google.. Wraenking just did a ton of searching on it (we're doing his rear section). LMC, JC Whitney, Chevy Duty and others carry the panels..
an up and running clean tub swap is not a quickie either, but usually the preferred method.. not really an option in lots of the country, i know they're aren't many in my state really.. "might" be worth a shot looking on Ebay for an Arizona, Cali one and shipping it.. maybe...
