Slick 60's

What's the best choice for sealing that mid-way horizontal seam on the firewall? Would POR-15 putty work? Or does it need to be an elastomeric type compound?

I used a brush on seam sealer from Eastwood.

I'm guessing this is it? https://www.eastwood.com/ew-brush-on-se ... quart.html

I used that brush on seam sealer as well. I used a tube style on my roof and a few other places.