How difficult is it to repair the under carriage on a car like the CRX?

eg: i crawled under there to make a temporary repair to the exhaust (so i can pass emissions) and i noticed that the two channels that run from front to back are rotting away... is this fixable?

I guess anything is fixable, but this is structural right?

What would i have to do, cut out the rotten part, fabricate a new "channel" and then weld it on?

What possible approaches are there to fixing this?

I'm not rich, but i'm not afraid of hard work.

 

clean off all the undercoating, down to bare-metal, shave all the rust out, all of it, cut it out if you have to, and them build new peices, and weld them in. then prime, and undercoat EVERYTHING.

honestly though, it probably isnt that big of a deal, but its very fixable, just do it right. probably wont be much work either, depending on how much is rotten away.

 

to weld this, the carpeting has to be removed right? I hate to ask noob questions, but i am in fact a 'noob' to restoration

can i just form carbon steel? OR i wonder if i can cut some square tuning in half and weld that in as the channels?