Metal Rib Ceiling trim for vertical B Vent

[m123]

I am installing the usual garage unit heater (Hot Dawg/Reznor/Big Maxx) and I have a metal ceiling ribbed ceiling. What have others used as a trim piece to cover the hole the B-Vent goes through? I assume since its a metal ceiling, its not combustible so I can cut the whole almost exactly the same size and won't need the 1" clearance, but I'm not sure I can get it exact and will need a trim piece anyway.

I considered a collar, but because of the ribs it wont sit flush. Maybe since its high enough it won't matter, but what have others done?

 

[alexb2000]

How about a spun storm collar inverted and coped to meet the ceiling?

I'm talking about a collar like this:

https://www.amazon.com/dp/B0085V01AK/?tag=atomicindus08-20

 

[Radix2]

Just the standard flat collar will,look fine - all your metal trim - j bead, etc does not follow the ribs so there is a shadow line/gap anytime you go in crosswise.

the fact that the collar has space behind it is not going to look odd on the ceiling.