Need Suggestion for Trim around SAFC Vent Mount

I've relocated the SAFC & TT into the center vent. I followed the typical fiberglass and bondo route, and it's turned out really well. The pieces slide in with about a 1 mm gap, so it looks good as is, but I'd like to pretty it a bit by putting black trim around each piece for an even cleaner & tighter look.

I'm not sure how to explain what I'd like to use, but think of an o-ring as an example... stretchy, skinny and elasticy. That thickness, but of course, it would have to be about a 3-4" diameter in order to stretch it around the SAFC and TT. (individually of course)

See example (not mine) pic below for what I mean.

Here's what I've thot of:
- black silicone, but I don't think it'll look right. It's gotta be just a thin bead around it, with no start or end point.
- a black rubber band, but has to be round, not flat.
- pinstriping, but I doubt the rounded corners would come out looking good.

Any other suggestions would be appreciated. Thanks.

Maybe you could cut some vacuum hose to size, with a slit along the length of it (probably take out up to half of it).

If you're careful enough with the lengths and the angles of the cuts, you could probably even get the corners to look good.

Get it to stay with some black RTV.

Put a thin sheet of something around the inside of the pocket. Blend it in with bondo. All you'll have left is a tiny gap, just like the stock stuff.

small vacuum line should look very good i think and would form around the contours well too.

Thanks guys.. great idea. And I just happened to receive my Princess Auto catalogue last night, so I'm heading out there this week!