I used the butyl rope and it looks so tacky! I think it solved the problem, but once it gets warmer I want to removed the box altogether and sand down/repaint the firewall (engine is already out). I found some rust holes in the firewall over by my windshield wiper motor (caused by gunked up leaves and such) and that definitely seems like the culprit over on that side.
Check it really good mine didn’t look that bad until I started digging deeper and found that even the cross brace that runs from pillar to pillar was almost rusted through. I believe the insulation and debris just held the moisture and just really ate it up with rust.