AC/heat box foam seal to firewall question.

[HAFROD]

I bought a new foam seal from OPG that goes between the firewall and the main box. Its a soft foam and worried about it sealing. Should I put something on both sides or just put it on dry? The factory seal I believe is more of a rubber than foam. Just unsure on what to use for sealing unless it don't need nothing but the seal https://www.opgi.com/monte-carlo/L240616/

 

[Longroof79]

I've never had my a/c box completely off, only for the top. I've used 3M strip caulk around the perimeter. I think it couldn't hurt to put a bead of strip caulk around the flange in addition to the new seal. That's just me.

 

[Blake442]

The factory used a brush on sealer around the outer perimeter of the heater box that dries up and cracks over the years.
I used an extra bead of 3M Strip-Calk around the box when I had mine apart.