I am going to be welding up various spots under my rear seat that WI salt decided to get up into and rust out. Section is roughtly 2-3" wide and maybe 8-9" long to cut out the part on top of a unibody support that runs under it.

When welding up the new material on top of this "box support" unibody thing, how does one paint and finish the new bare metal inside the closed box when they are done to prevent future rusting? Would it be wise to drill a few small holes in the box, and paint through it and blast up in there?

Right now 100% of my welding has been with a hobart mig, but no gas cylinder yet. I have been using flux core stuff, and am quite aware that it puts off lots of foul ash type crap around the welds that needs to be cleaned off before painting. If you use a good shielding gas, is there any of this to deal with if I were needing to paint right after I did a weld for a section I couldn't really get into the best?

 

Prepaint all but the areas around where the weld will be. Any holes you make will alow for water to get up there. The only real way to get it painted well is powder coating....

 

Well any holes will be getting rubber plugs put in after I am done, so water isn't an issue. Powdercoating isn't an option as I can't really bake my car

 

Yeah, well that was kind of my point. I really don't think there is a good way of doing it.

 

You could drill a hole and pump some liquid restolieum into the hole (instead of via rattle can)

 

Well if I was going to paint it, I would get a extension nozzle thing for framework and use that to pressure spray the inside.

I just want to know about residue and stuff left over after a true clean mig weld.