I let the rear most cross sill fry while I was at work today. I kept having to flip it around through out this whole process to get line-of-sight between it and the sacrificial piece of metal.
Overall it did real good, rust floated off like butter, I hit it with a wire brush for about 15 minutes then took it to the car wash and power sprayed it, then back home and air dried it with the compressor hose.
A little got left inside the channel because it was just hard to hang it right so that line of sight from the sacrificing metal could see in there. Next pic shows my idea to fix that on the other cross sills... and I may hit this one another time using that idea if I can't get at that little bit with a wire wheel and drill.
I just ran a piece of metal inside the channel and made isolators from a plastic trash bag rolled tight and wrapped in electrical tape. The inside of this channel doesn't stand a chance.
