how should I attack the rust in this area
I'm not too sure about the ospho not getting in those tight bends. I worked at Jim Vince Dodge body shop on fort street lincoln park Mi.and we got to go to where they made the sub assemblies we had to fix. IE doors/hoods/trunk lids ect. and they were just machine bent to the sub-frame assembly with a couple of tack welds to prevent shifting, exactly like a door skin. sometimes they had a "putty the oozed over into the edges but for the most part it's just a bend over an edge. Rust in that area is just as easy to have the thin liquid ospho seep into as any other inner area. that is why I always duck tape closed all but one hole , pour in the ospho tape that hole and rotate the part every which way to coat the inner surfaces.(you should see what a 2/3rds yard cement mixer with a hood strapped on it rotating looks like) I've got a 65 Plymouth hood that was in worse shape that that hood and it has not shown rust through in 13 years of being driven most days of the warm driving weather in Michigan. looks just as good as the day after we oshpo'd /painted it. doors were done too and have never shown any sign of rusting through even on the lower edge.
I'm not too sure about the ospho not getting in those tight bends. I worked at Jim Vince Dodge body shop on fort street lincoln park Mi.and we got to go to where they made the sub assemblies we had to fix. IE doors/hoods/trunk lids ect. and they were just machine bent to the sub-frame assembly with a couple of tack welds to prevent shifting, exactly like a door skin. sometimes they had a "putty the oozed over into the edges but for the most part it's just a bend over an edge. Rust in that area is just as easy to have the thin liquid ospho seep into as any other inner area. that is why I always duck tape closed all but one hole , pour in the ospho tape that hole and rotate the part every which way to coat the inner surfaces.(you should see what a 2/3rds yard cement mixer with a hood strapped on it rotating looks like) I've got a 65 Plymouth hood that was in worse shape that that hood and it has not shown rust through in 13 years of being driven most days of the warm driving weather in Michigan. looks just as good as the day after we oshpo'd /painted it. doors were done too and have never shown any sign of rusting through even on the lower edge.