thanks for a sensible answer from the vk4, is it ok mounted in a metal case as long as the banana posts for the ladderline are insulated from the box, Also can i wind it the same as in the pic i posted, Same number of turns etc?.
I do not have a suitable answer to that. My gut says it depends. I mean, think of an antenna tuner, the old school balanced ones, big air caps, big roller inductor, big balun all sitting in a metal box. They do not seem to have a proximity problem, will a metal can effect a big toroid? I do not know, maybe, but I honestly think it wont make a difference, ferrite is not overly conductive, being in proximity to other metal probably wont have much of an effect on a 1:1 balun at all, 4:1 and other combinations it might have a slight de-tuning effect.
I do not have any good reference books here to lookup to get a better answer than that, but the last thing you want is for that metal can to become an antenna and start radiating, so for that reason along, i put things like baluns and my remote tuner into plastic. I hate antenna debates because there is a lot of voodoo out there and fan boys ranting and raving about stuff that has no basis in reality.
Long answer where answered nothing, other than to say, I would go with plastic out of precaution, but seeing tuners have metal cases and baluns in them, its probably not a problem. Try it and see what is what. The internals should be floating anyway and the case not part of the transmission line.
Yes wind and build as per your image.