I have some rust underneath on the pinch welds of the sub frame. do you think I could get away with wire brushing the heack out of them, then spraying it all down with rust converter?

 

I sandblasted mine, but wire brushing should work OK. With wirebrushing it might be a little tough to get to all of the rust. I used POR15 followed by black engine enamel to prevent rust from making a return. The key is to make sure that everything is clean before applying anything...get rid of all the loose scale, dirt, undercoating, etc. Make sure you apply the rust preventative in all of the nooks and crannies where water can hide. I check the underside of my GTA every year and treat any areas that start looking suspect before they turn into more serious problems.