retrofit vinyl windows- using wood trim on inside

pman6

I often see installers use vinyl strips to finish and cover the gap between the existing metal window frame and the new vinyl window frame, seen from the inside of the room.
Looks tacky to me.

I was thinking about using 1/2-3/4" fiberboard to create a sill to obscure the gap, plus finish with moulding around the edge, like pic below..

Is it ok to butt the fiberboard/plywood against retrofit vinyl window like that?
Will there be expansion/warping issues?

Windows on Wash

Totally fine.

Don't smash it into it, but leave yourself a small caulk joint.

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kwikfishron

Use a siliconized acrylic latex caulking.

Do not use 100% silicone caulk.

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