It doesn't look like you've removed much of the rusted metal which means you're trying to join good to bad. It also looks like your patches may be coated steel (zintec?) which will also give you problems welding. If it was me I'd possibly take the patches off and clean as much of the area as possible. Looking at one of them it doesn't appear that you have much penetration, just 'blobs' on the surface. You might want to up the power a little and maybe up the gas slightly too, this might help you get a flatter stronger weld requiring less grinding back. Regarding getting into tight corners, basically any way you can really, an angle grinder can be pretty cumbersome in tight spots.
. The coating won't help at all but if you're grinding it off then you should be getting better results than you currently are. I honestly think it's more to do with your preparation. What machine are you using? What wire and gas and how old is the wire? All these things have a bearing on the quality of your welds.
Skoobs, I wasn't even remotely having a dig, just trying to assist
