Re: toroid parts...
Two things. First, I have seen similar trash can lids
and come up with the same thoughts. There is always the "midnight
requisition" route, and those things must get beat up and replaced
Two, the flexible ducting works fine as-is. If you
wrap it with either aluminum tape or just plain masking tape
(to be followed by an overall layer of aluminum tape) you will
find the assembly is plenty rigid enough to handle without anyu
any filling at all. Have tried three inch to six inch ducting,
and found it was much sturdier than I expected. Give it a try!