Yea steel cones will work.  Make sure they are good and tight.  All fertilizer tanks we have are steel, liquid or dry.   Some will suck moisture up from bottom and you could have a mess, I mean no mess, nothing will come out.

You getting one blend for all year or you storing 3 products.  Your local dealer would most likely fill your wagon and cart in a timely manner.  I guess we hardly use the same blend for everything  around here.