Advice: Gas Insert Retrofit

Hello everyone! Looking for advice on this retrofit I did in my home. It was built with a builder grade Majestic 336 (IIRC) with a b-vent that ran through a wooden framed / uninsulated chase and terminated roughly 5 feet off the roofline.

I pulled it & removed all of the tiling/front-face from the fireplace. Decided on the Oakville X4 -- ran the two 3" collinear liners up the chase & terminated with a cap.

I tried to follow the manual closely which specified creating a plate to prevent drafts. This made sense to me given the massive amount of air volume in the chase. So I built a small frame with steel studs & a galvanized plate roughly 6" above the unit. On top of this I packed it with rockwool.

There's at least 4" of air gap around each side of the insert (significantly more on top), with a tile hearth extending 12" below.

I've been running it & checking the frame with a temp. gun, looks like the wooden framing is sitting around 95-100 degrees F, 3" exhaust at ~ 260 degrees F, intake 130.

Here's a photo: [img]https://i.imgur.com/B7BnUNw.jpeg[/img]

My question: Does this look ok? I am slightly worried given how much more heat this unit puts out vs the old. Is it ok to have the rockwool packed tightly on the exhaust pipe specifically? I'd like to get some thoughts before installing the cement board/tile over the gaps. Thanks in advance!